In a medium pan over medium-high heat, add 4 tablespoons of butter.
When the butter is melting and starting to bubble, add all of your flour. Stir constantly for 1 to 2 minutes to combine everything while both the butter and the flour cook.
When the butter and the flour are fully combined and are in a paste-like form, start adding your turkey stock a little bit at a time while stirring. If you have a whisk that will not scratch up the surface of your pan, start using that to whisk everything together.
Continue adding the stock a quarter or a half cup at a time while whisking/stirring. At this point your goal is to make sure there are no lumps from the flour clumping together. If you see lumps, mash them with your whisk or spoon to try to break up any clumping flour. If you added the stock slowly and stirred enough you will not have lumps.
Once all your stock is added, add a small pinch of salt and black pepper.
Add in any pan drippings you might have from cooking your turkey. If there are no pan drippings, you can still have good gravy, it just won't be quite as flavorful.
After your pan drippings are added, you should taste the gravy for seasoning and add any extra salt and pepper that you think it might need.
Now that all of your ingredients are combined and stirred in, cook until you get to the consistency of gravy that you desire, stirring occasionally.
At this point your goal is to look for your favorite gravy consistency. The longer you cook it, the thicker it will become. Once it's as thick as you'd like, remove from heat and serve. Remember: the gravy will continue to thicken a little bit after removing it from the heat, so it's best to shoot for just below the thickness that you desire.
Notes:
If you attempt to reheat gravy the next day, it will become extra thick. The best thing to do in this situation is add a bit more turkey or chicken stock and reheat in a pot on the stove. You can do this in the microwave too, if you just need a little bit of gravy.
If you don't have chicken stock when attempting to reheat gravy, you can use a little bit of water.