In a medium saucepan, melt butter over medium-high heat.
Once the butter has melted completely, whisk in half the flour. It will make a thick paste. Let cook for 1 to 2 minutes.
Slowly pour in stock and whisk well, stirring continuously for 5 minutes.
Whisk in remainder of the flour and keep stirring until gravy is thick and creamy.
Remove gravy from heat and let it stand for 2 to 3 minutes before serving.