2 tablespoons bacon grease (or vegetable oil)
1/4 cup all purpose flour
3/4 teaspoon salt
3/4 teaspoon coarse ground black pepper
3 to 3 1/2 cups whole milk (substitute cream for some or all of the milk if you like)
In an 8-inch cast iron skillet, over medium-high heat, add bacon grease. When grease is melted, add flour, salt and pepper, whisking until all combined. Whisk occasionally as flour mixture starts to brown. You want it to get golden brown, but be careful to not let it burn. Gradually whisk in 3 cups of milk, and continue to whisk until it is thick and starts to bubble, adding more milk if it gets too thick. Lower heat and keep warm until serving.