Preheat oven to 375°F. Lightly grease a 9x13 baking dish.

Mix together the garlic herb cream cheese and ½ cup grated white cheddar until combined. Stuff each mushroom cap generously with this mixture.

Make the Alfredo: Melt butter in a saucepan over medium heat, add garlic and cook 1 minute. Whisk in flour, cook 1 minute. Gradually add heavy cream and half-and-half, whisking constantly. Add Parmesan, white cheddar, and Gruyère, stirring until melted and smooth. Season with salt and white pepper.

Pour the Alfredo sauce into the bottom of the baking dish, add about half of the sauce, you want to add enough to just cover the pan.

Nestle the stuffed mushroom caps (filling side up) into the sauce.

Spoon a light layer of sauce over the top of each stuffed cap.

Cover all mushrooms with the remaining 1 cup of white cheddar cheese.

Mix melted butter, breadcrumbs, and garlic powder together. Sprinkle over the cheese layer.

Bake 10–12 minutes until mushrooms are tender, and cheese is bubbly.

Switch to broil on low and broil for 2–3 minutes, until the breadcrumbs are golden. Watch closely so it doesn’t get too browned (must be golden brown).

Garnish with fresh chopped parsley and serve immediately from the pan.