Start your gravy with a roux—a mixture of fat such as pan drippings or melted butter and an equal amount of flour whisked together and cooked until golden. This thickens the sauce and gives it some colour. The darker the roux the darker the gravy. Use a whisk or a wooden spoon to combine the ingredients.
Add stock slowly so that you get the desired consistency, which should lightly coat the back of a spoon. This also prevents lumpy sauces.
Do not season until the gravy is finished because reduction brings out the natural saltiness of the stock.
Do not add more flour if the gravy is not thick enough. It will be lumpy. Make a slurry using equal parts cornstarch and cold water and add the slurry, a teaspoon at a time, stirring, until the gravy reaches desired thickness.
To add a glossy sheen to gravy and give it a velvety texture, add a teaspoon or two of butter at the end.