I am not a great cook, but I excel at making gravy. Sunday biscuits and gravy was one of the few food-related family traditions we ever had in our home. My friend who would "bring shame to her family" if she ever used canned beans (excellent cook), uses powdered gravy because she has never figured out how to make gravy. Puzzled, I thought to myself...what is so hard about gravy? Then I wondered more seriously...What IS so hard about gravy? I discovered that what is 2nd nature to me after a lifetime of gravy indoctrination actually has many pitfalls! I have hacks that I never regarded as "hacks" and here they are...
Warning! Don't expect a recipe. The thickness and consistency has to be adjusted as you observe how the gravy is behaving. You can find recipes all over the internet and YouTube to get an idea of estimated proportions.
Meat broth is essential to your gravy success. Bones make the best broth. Anytime I cook meat, I de-glaze the pan with water and save that liquid for soups and gravy. My husband refers to my broth as "juice." We frequently cook a whole chicken in a crock-pot. We like to have unflavored, shredded chicken on hand for quick meals. The boiled meat is rather bland because the flavor is now in the BROTH! The remaining greasy golden liquid we call "chicken juice." It has no onion, celery, spices, or additions besides salt and black pepper, so it is very versatile and therefore rightly referred to as juice.
Oven roasted ham, turkey, beef leftovers always find their way into a soup, stew, or gravy in my house. After harvesting the edible meats from a turkey dinner, the carcass/neck/giblets/skin/fat/drippings all get pushed down into the roasting pan, water to nearly cover and back into the oven for a couple of hours to create broth magic! Using far too much water will make a thin broth with mild flavor. I prefer intensely flavored broth that gels firmly (as it is easy to dilute flavors, but difficult to boost later). I transfer the resulting meat juice (be it beef, pork, ham, turkey, shrimp tails, etc) into a microwave-safe plastic bowl and refrigerate overnight so the fats separate and float to the top in a thick lardy layer. Then into the freezer with a label with date and animal. Small yields from de-glazed pans which often have more flavors from spicy dishes may go into a ice-cube tray which I later transfer to a freezer-bag. These ice cubes often go into mixed vegetables so I don't mind if they are not "clean meat juice" and have additional flavorings. Larger amounts of broth that have vegetables or spices may be better utilized in soups and stews than in gravy, but might compliment a gravy and give a desirable depth of flavor. Straining of bones and bits need to be done at some point, but I will let you decide at which stage you do this.
My first hack is BIG! Do not attempt to use the drippings from what you are currently cooking! Use broth from a previous meal! Refrigerated or frozen broth will change your life! Straight out of the freezer you can scrape off the lard. Lard layer can be lifted off of refrigerated broth with a fork, but you will have to pat dry with a paper towel to remove all wet broth gelly or you'll have popping grease during the next step. Brown your flour in that lard in a skillet or sauce pan. Later, when I tell you to add only cold liquid to your rue, you will be grateful you aren't having to cool down the hot drippings from your current project to make gravy. It allows you to control how much fat goes into your gravy so it isn't greasy. And this allows you to prepare the gravy AT ANY POINT in your cooking process instead of having to wait until the meat is done resting in it's own juices to remain moist. You'll thank me when you get to my instructions to stir constantly without distraction to avoid lumps (nearly impossible to do while throwing the finishing touches on your meal moments before serving!) NOTE: The smaller the mouth is on your plastic container, the thicker your lard layer will be.
Make a loose rue for even browning, and then add a tablespoon or so of flour to thicken the rue until it is clumping up on the spoon but all the flour gets 'wet' with oil. Ensuring that the lard is all spent into the flour will keep you from having greasy gravy even if you have to use fresh broth that hasn't separated in the next step. I like a deeper browning for beef and a lighter for all others, but you do need it to be fragrant and show a color change. The deeper browned rue will thicken broth less than lighter rue will so you may need to adjust your broth measure. (Rue is your flour/lard paste.)
Lard vs Oil
I always use home-harvested lard for my gravies (not that snow-cap stuff that comes in a tub). Bacon grease is fantastic for milk gravy. I don't recommend using broth and lard from two different animals, except turkey and chicken which I use interchangeably. Duck Fat might be another exception to that rule, but I have limited experience with it. Butter can be used with many meats, but you must tolerate the browned butter, "nutty" flavors that will develop as the milk solids brown while making your rue and may burn in a darker rue. Vegetable oil won't add any flavor, so I would opt for an intensely flavored oil like extra virgin olive oil or coconut oil...but you can see these would color your entire meal, and you should restrict their uses to meals where they would complement rather than overpower.
Flour vs. Cornstarch
Cornstarch adds no flavor, and is strictly a thickening agent. I find that I have to add other flavors to cornstarch gravies such as Kitchen Bouquet or Worcestershire (for beef or venison only), but I love making a light gravy for roasted chicken with lemon and either rosemary or a hint of lavender. Giblet gravy is an acquired taste, but it is best with cornstarch. I like giblet gravy if the giblets are pureed. If I totally goof and make really runny gravy that won't thicken any more no matter how long I cook it...I will add a slurry of cornstarch and cold water. Flour adds its own flavor if used correctly. Always brown flour to some degree in a rue. Flour and water slurry is going to add an unpleasant flavor--I would not do this unless it was do or die. Flour will make an opaque gravy, whereas cornstarch gravy will be translucent. If I have to use the drippings from the meat I am currently preparing, I will opt for cornstarch so that I don't end up with a double portion of fats (lard from a rue plus the fats suspended in the new broth). Gravy is greasy enough without being greeeezy! TIP: You can cool the hot drippings and help fat to separate (and be skimmed off for the garbage or for the rue) by adding the iced broth cubes you've stored up previously!
Additions of water may be necessary because of the intense saltiness of ham drippings or bullion additions, but beware that water will dilute any flavors you've built into the gravy so far. For most gravies, broth is a better choice to thin out the consistency (or milk in milk gravy). Chicken broth is a nice way to extend your turkey drippings which never seem to yield enough drippings to make a generous batch of gravy. And let's face it, you don't want to eat turkey leftovers once you've run out of gravy! Any liquids you add to gravy or rue, including water, should be COLD and incorporated quickly by vigorous stirring.
Adding Broth to Rue
As soon as your rue is browned and thick, drop whatever you are doing! Make certain nothing else is going to divert your attention! Tell everyone you are starting the gravy and cannot be bothered! Recruit help in the kitchen to attend to the bread that is soon to come out of the oven! Ready?! Add COLD (but thawed) broth in generous amount to your rue paste and whisk like it's your job! At first, it will seem that the cold liquid and rue clumps aren't mixing. Medium heat is fine. Just keep stirring. As the mixture warms up, the motion must pull away warm layers from the clumps gradually. As the liquid gets cloudy and homogeneous, you can slow down a bit on stirring, but if flour settles to the bottom of the pan you risk lumps. If you still have lumps of rue, and the liquid is "gravy thick," add more COLD broth. When all of the flour is properly suspended, you have gravy! Taste for salt content and adjust flavors. Make sure to allow it to bubble for a full minute. If the gravy is a little thin, cook a little longer to reduce. This will concentrate flavors. If the gravy is very thin but the rue lumps have completely dissolved and it has bubbled for 1 minute, you need to remove from heat, and add a slurry of cornstarch and cold water. Try 1/2 Tablespoon of starch to 2 Tablespoons of cold water--you only want to introduce enough water so that the cornstarch can be dispersed completely into the water. Pouring your slurry through a fine sieve will ensure you aren't adding lumps (Add lumps, get lumps!). Add the slurry to gravy all at once and whisk like a mad woman to avoid lumps forming). Once incorporated, set back on stovetop at medium heat and make certain everything bubbles for a minute. Once you serve the gravy it will start to cool and thicken. Often more liquid must be added when reheating refrigerated gravy as the starch reaches maximum absorption.
For milk gravy, just treat milk as your "broth" and follow these same instructions. Add pork breakfast sausage (not the maple kind!). Sage, black pepper, and red chili powder make it mine!
For green chili, make your gravy with pork lard or vegetable oil (I know, I said not to use oil!), and pork broth. Add cooked pork meat (chunks or shreds), diced tomatoes, and diced roasted green chilis!)