Preheat your oven to 375°F (190°C) and prepare a cast iron skillet with nonstick spray.

Clean the mushrooms with a damp paper towel and twist off the stems to create cavities for stuffing.

In a mixing bowl, combine breadcrumbs, melted butter (3 tbsp), coarse sea salt, and black pepper.

In a skillet, melt remaining 3 tbsp butter, sauté minced garlic, add flour to create a roux, then whisk in half and half and Parmesan cheese.

Layer half of the Alfredo sauce in the skillet, place mushroom caps on top, and spoon remaining sauce over each mushroom.

Sprinkle grated white cheddar cheese and reserved breadcrumb mixture over the mushrooms.

Bake for about 10 minutes, then broil for 2-3 minutes until golden brown.

Garnish with chopped parsley and serve warm.