Melt 2 tbsp. butter in non-stick frying pan. Add potatoes, salt and pepper. Saute until golden brown (about 20 minutes). When potatoes are close to finished, melt 1 tbsp. butter in a separate frying pan and saute corned beef about 3 minutes. Add garlic, onion & bell peppers and sautée for 3 more minutes. Add mustard to corned beef/onions/peppers and mix well. Combine potatoes with meat and vegetables. Mix well and serve.