Rinse the mushrooms lightly to clean them, but don’t use too much water. You don’t want them to get soggy.
Carefully break off the mushroom stems (they should come off easily, or you can cut them). Set them aside and toss them into a vegetable stir-fry, vegetable stock, lo mein, or an omelette!
Pat the mushroom caps dry with a paper towel, and arrange them neatly on a sheet pan with the cap side up.
Heat 6 tablespoons of butter in a small saucepan over low heat until it’s just melted. Remove from the heat.
Use a brush to lightly brush the mushroom caps with melted butter, turning them over afterwards so they are top-side down.
Preheat the oven to 375 degrees F. While the oven is preheating, make the stuffing. Stir ½ teaspoon onion powder, ½ teaspoon granulated garlic, 1 teaspoon dried thyme, ½ teaspoon paprika, and ¼ teaspoon salt (or to taste) into the butter until well combined. Use a rubber spatula to mix in ¾ cup plain or Italian breadcrumbs until all the breadcrumbs are saturated with butter.
Add 1/3 cup grated parmesan cheese and 1 tablespoon finely chopped fresh parsley, and stir to combine.
Stuff a spoonful of breadcrumb mixture into each mushroom cap but don't pack or compress the stuffing which will keep your stuffed mushrooms light and flaky, then bake them for 9-12 minutes. The mushrooms should be cooked through, but firm enough to pick up with your hands. You don’t want to overcook them, or they’ll be droopy and hard to handle.
Serve immediately and enjoy!