In large skillet, heat 1 tbsp. olive oil with 1 tbsp. of butter over medium low heat. Add cabbage. Cook until soft and edges are beginning to brown. Remove from pan & set aside.
Using the same skillet over medium heat, add 1 tbsp. olive oil and bangers. Cook until browned on all sides and cooked through. Remove from pan & set aside.
Boil potatoes in medium saucepan until soft. Add milk, 2 tbsp. butter and salt & pepper to taste.
Add cooked cabbage to potatoes. Cover & set aside.
Add onions to skillet. Cook over medium heat until transparent and caramelized. Add 2 tbsp. butter and flour to pan. Stir until onions are coated. Add beef stock, bouillon and whole grain mustard. Simmer over medium heat until thickened. Season with salt & pepper. Return bangers to the gravy pan to reheat.
To serve, arrange bangers on top of colcannon. Drizzle with gravy. Sprinkle with scallions.
