Melt the butter in a skillet over medium heat. Whisk in the flour and cook until golden, 1 to 2 minutes. Whisk in the warmed stock. Bring to a simmer and cook, stirring constantly, until thickened, 10 to 15 minutes. The mixture should coat the back of a spoon. Pour in the wine, stir and cook for an additional 2 to 3 minutes. Season to taste with salt and pepper.