Bread:

• 1 loaf Italian bread, sliced lengthwise
• ½ cup (1 stick / 113 g) unsalted butter, softened
• 1 teaspoon garlic salt

Chicken:

• 2 boneless skinless chicken breasts (about 1 pound total), cut into ½-inch pieces
• 1 tablespoon blackened seasoning (store-bought or homemade)
• 1 tablespoon extra virgin olive oil

Alfredo Sauce:

• 2 tablespoons unsalted butter
• 1 small yellow onion, diced (about ½ cup)
• 2 teaspoons garlic, minced
• 2 cups (476 g) heavy whipping cream
• 2 cups (200 g) Parmesan cheese, finely grated
• ½ teaspoon kosher salt
• ½ teaspoon black pepper
• ¼ teaspoon crushed red pepper flakes

Topping:

• 1 cup (113 g) mozzarella cheese, shredded
• 1 cup (113 g) white cheddar cheese, shredded
• Fresh parsley, chopped, for garnish