Heat the bacon grease in a large skillet over medium heat.
Whisk in the flour until there are no lumps. Cook for 1-2 minutes to get rid of the raw flour taste.
Slowly whisk in 1 1/2 cups of the warm milk. Once all the milk is incorporated, bring to a boil and cook until thickened, whisking frequently. If the gravy is too thick, add more milk until your desired consistency is reached.
Stir in the crumbled bacon. Taste the gravy and add salt and pepper as needed. You may not need much, if any salt, depending on the saltiness of bacon grease.
Serve warm over biscuits with eggs, fruit, or your favorite breakfast items.
Notes
Cooking time includes 10 minutes to cook the bacon. The 4 slices used for this recipe should yield around 1/4 cup of bacon grease. If needed, you can supplement the amount of grease in the skillet with leftover bacon grease (if you save it for later) or some butter until you have 1/4 cup total.