Pot Roast Nachos

Bahan-bahan (8 porsi)

• 2 tablespoons butter
• 1 large sweet onion (or yellow onion, sliced ¼-inch)
• 2 (24 ounce each) bags waffle fries
• 2 cups cooked beef (pot roast, leftover steak, prime rib etc, chopped or shredded)
• 1½ cups shredded mozzarella cheese
• ½ cup shredded gruyere cheese (or provolone, or additional mozzarella cheese)
• ½ cup frozen peas
• 1 cup beef gravy
• ½ cup horseradish sauce