For the cheese filling, combine cream cheese, garlic powder, Italian seasoning, and parmesan cheese in a mixing bowl. Mix until combined.
Set it aside for now.
Preheat the oven to 400 degrees and line a baking sheet.
Clean the mushrooms and remove the centers. Drain using a paper towel.
Drizzle olive oil on the mushrooms, coat with garlic powder, and add a pinch of salt.
Stuff the empty centers with the cream cheese filling.
Place the mushrooms on the baking sheet.
Roast the mushrooms for 10-15 minutes.
In another bowl, combine the Worcestershire sauce, flour, white wine, half-and-half, mayonnaise, pepper, and dry mustard.
Mix well, and add the white cheddar cheese. Transfer to a pot.
Heat over medium heat, and let it simmer until the mixture is creamy.
Pour in the white cheddar sauce, and place the mushrooms on top.