Onion-Mustard Gravy for British Bangers and Mash
- Melt butter in a heavy-bottomed pan over medium heat. Cook and stir onion in the melted butter until softened, about 10 minutes.
- Reduce heat to low. Cover the pan and cook until onions are caramelized, stirring occasionally, about 20 minutes.
- Stir flour into the caramelized onions and cook for 1 minute.
- Pour red wine, chicken stock, Dijon mustard, and Worcestershire sauce into the onion mixture; simmer until sauce is thickened, stirring frequently, about 15 minutes.
- Season to taste with salt and black pepper.