Sprinkle with salt and pepper and slowly whisk in flour. Cook until the flour is fully incorporated into the butter and gravy is your preferred color.
Once that stage is reached, constantly whisking, slowly pour in the turkey stock, and cook until the gravy is thickened.
If serving from made-ahead turkey gravy, reheat in a medium saucepan until warmed throughout. If the gravy is too thick, add more stock until it reaches the desired consistency.