Ingredients 

For the Butter: 

1/2 cup butter, softened 

1/4 cup grated Parmesan cheese 

1/2 teaspoon garlic salt 

For the Grilled Cheese: 

8 slices Ace Bakery Sourdough Bistro Bread 

6 slices white cheddar cheese 

6 slices mozzarella cheese 

Instructions 

1. Prepare the Butter: In a small bowl, mix together the softened butter, grated Parmesan cheese, and garlic salt until well combined. 
2. Assemble the Sandwiches: Lay out the 8 slices of sourdough bread on a clean surface.Spread a generous amount of the prepared butter mixture on one side of each slice of bread. On the unbuttered side of 4 slices, place 1 1/2 slices of white cheddar cheese and 1 1/2 slices of mozzarella cheese. Top with the remaining 4 slices of bread, buttered side facing out.
3. Grill the Sandwiches: Heat a cast iron skillet or a heavy-bottomed pan over medium-low heat. Place the assembled sandwiches in the skillet, ensuring they are not overcrowded (you may need to cook in batches). Press down gently with a spatula to ensure even grilling and to help the cheese melt. Cook the sandwiches for about 3-4 minutes on each side, or until the bread is golden brown and crispy, and the cheese is melted and gooey. Slice in half and serve immediately.