Mushroom and Onion Grilled Cheese Recipe | Wisconsin Cheese

Ingredients

• 1 medium onion, halved and thinly sliced
• 1 tablespoon olive oil
• 1/4 teaspoon each salt and pepper, divided
• 4 tablespoons butter, softened and divided
• 1 1/2 cups sliced mushrooms
• 1 garlic clove, minced
• 1 to 3 tablespoons stone-ground mustard
• 6 slices rye bread
• 4 ounces Widmer's Mild or Aged Brick cheese, shredded (1 cup)