Drain the rendered pork fat out of the pan, reserving 2 tablespoons.
Return the pork fat to the pan. Stir in the white wine, scraping any browned bits off the bottom of the pan. Bring the wine to a simmer & cook until the liquid has reduced by half.
Stir in the mustard and chicken stock. Continue to simmer until the sauce has thickened enough to coat the back of a spoon.
Turn off the heat & slowly whisk in the butter, one cube at a time.
Keep the sauce warm until you’re ready to serve.