There are a lot of make ahead gravy recipes and I tried several. They were mostly tasteless. So I began adding ingredients and changing things around. This makes a really good turkey gravy. I know it seems like a lot of work, and it is. But if it's done a week or so ahead, you have it done and ready and no last minute rush.
NOTE: Keep the leftover turkey and veggies in a zip lock in the freezer. Remove the fat, gristle and bone and freeze. You can use this to make turkey soup or pot pies. Please don't share with your dog, the onion is not good for them. :)
Preheat oven to 350. Place turkey parts, carrots, celery and onions in a large bowl and cover with 3 Tablespoons of olive oil, toss to coat. Place all on a large cookie sheet and bake for about an hour until turkey is browned on top.
Place all in a large stock pot, add water, 2 quarts of turkey broth, bullion cube, garlic cloves, thyme and bay leaves. Simmer gently for abut 2 hours, then add the last carton of turkey broth and continue to simmer for about another hour until the meat falls off the bone. As it simmers, skim off some of the fat. I use a fat separator to make it easier. Set aside 3 to 4 Tablespoons of turkey fat. Strain the liquid. You should have about 10 cups. If not, add water or a can of broth to make 10 cups.
Here is the tricky part. Make a ROUX. In a large pot, like a Dutch oven, melt 4 Tablespoons of butter over medium heat and add the strained turkey fat. Add the 3/4 cup of flour and cook, stirring constantly until the flour begins to brown. The secret is to cook the flour in the fat, otherwise your gravy will have a floury taste. Once the flour is browned, slowly add the broth, whisking or stirring constantly. You should not have any lumps. Continue cooking and stirring over medium heat until the gravy begins to bubble. Once it starts to boil, it will not get any thicker. Once it cools, store in freezer.
Thaw in fridge then keep warm in the crock pot. When the turkey comes out of the oven, separate the fat then add the turkey drippings to the gravy for even more flavor.