The Basic Recipe
Put some hot grease in a pan.
Mix in some starch.
Gradually stir in some liquid.
Details
This is a cooking fundamental, the basic recipe for a whole bunch of sauces. For example, to make a white sauce, you stir flour into melted butter and then slowly add cream. The oil and starch get bound together, so that when you add water, both of them dissolve and make it thick and tasty.
Any kind of oil will work. I haven't tried starches other than wheat flour -- you'll have to experiment on your own. I mix in enough so that it's roughly as thick as gravy. The pan should be on low heat, so the flour and oil don't burn, but you can let it cook a minute to toast the flour a little. Then begin adding the liquid.
For some reason, when you add water to a hot oil-flour mixture, at first it makes it
thicker. You'll have to add quite a lot before it starts getting thin again. Also, unless your liquid is already hot, it's going to cool down the pan and you'll want to turn the heat up to medium or even high, depending on how fast you're adding it. The limit to how fast you can add the liquid, is how fast you can stir it in. If you add it too fast or don't stir it enough, your gravy will be lumpy. When you get the thickness you want, you're done, unless you want to add more flavorings.
Meat Gravy
It's possible that you'll have the perfect amount of fat and water-based drippings right there in the roasting pan, but probably you'll have to add some of both. When I'm making turkey gravy at Thanksgiving, it usually goes something like this:
In a large pan, melt about a half stick of butter, and stir in about a third of a cup of white flour. Add some pepper, and keep the temp low so the flour doesn't burn.
Now add the fat from the turkey drippings, or if you've boiled some turkey scraps on the side, skim the fat from the top and add it. Then add more flour. You want the flour-oil mixture to be roughly the same thickness as the gravy will be at the end.
Now slowly add the water-based stuff. This could be broth from a carton, broth from mixing water and bouillon, broth from stewing meat scraps (giblet broth adds a lot of flavor), or the pan drippings.
If you have a lot of pan drippings, it's good to pour them into a bowl or large glass, so that the water and oil will separate and you can skim off the oil and add it before any water gets added. If you add oil to the gravy after you've started adding water, the oil will not be bound up by the flour, and your gravy will be oily.
Make sure the pan drippings don't burn, because they're what really gives flavor to the gravy. If they're dry and concentrated in the pan, add some broth and stir it around to dissolve everything, maybe two or three times to get it all.
Keep adding broth/drippings until the gravy is the thickness you want. Then taste it and add salt if necessary.
Veggie Gravy
Vegetable broth that comes in cartons is seldom concentrated enough to make good gravy by itself, and it's not a good value. The best thing is to pack a lot of actual vegetables in a big pot of water or pressure cooker and boil it into strong broth. You could also try powdered dehydrated vegetables if your local food co-op carries them in the bulk section. I recommend onion powder because it has good gravy flavor and it's relatively cheap. Also add whatever spices you like. Nutritional yeast tastes great in gravy, but it's high in purines, which cause gout.
Now, to make the gravy, you heat up some fat of your choice. I would use olive oil, butter, or lard. Then add flour or some experimental starch, and gradually add broth. If you're using powdered veggies I've found that it's best to add them about halfway through adding the water. Too soon or too late and they get lumpy. Also you can pre-dissolve them in hot water. Leafy spices and black pepper can be added at any time, but I like to put them in the oil at the beginning, so that their fat-soluble components get dissolved and distributed better.
Mushroom Gravy
Get a lot of mushrooms, slice them up, cook them in a
lot of oil, and when most of the water is cooked out, add your flour, and then water or broth or a carton of mushroom broth.
(last updated november 2018)