8 portions of fish fillets
1/4 lb. butter
2 onions, chopped
2 cloves garlic, minced
juice from 2 limes or lemons
3 Tbsp. spicy mustard
salt and pepper to taste

Melt butter in a saucepan. Add onions and sauté until clear. Add garlic, lemon/lime juice, mustard, salt and pepper.

Preparation time: 15 minutes. Cooking time: 10 to 15 minutes.