Melt butter in sauté pan; add onions. Cook, stirring, until onions are caramelized.
Roast or grill Polish sausage until cooked through; cool. Cut into medium dice.
Heat Extra Melt® Cheese Sauce in double boiler to 165°F. Stir in caramelized onions, sausage, pickled peppers and mustard. Heat to 140°F. Hold hot or chilled until service.