Melt 2 tablespoons butter in a saucepan over medium heat
Whisk in 2 tablespoons flour
Cook the mixture for 1 to 2 minutes, stirring constantly
Slowly whisk in 1 to 1 1/2 cups broth or stock
Stir until smooth and thickened
Add salt and black pepper to taste
Simmer for 2 to 3 minutes
Stir in a splash of milk or cream if you want it richer
Pour over mashed potatoes immediately