24 large mushrooms, stems removed
1 pound Dean’s sausage
1 can diced water chestnuts, drained
1 onion, diced
4 ounces grated Parmesan cheese, divided
1/4 cup Italian bread crumbs or Panko
1 teaspoon minced garlic
1 teaspoon chopped fresh parsley
Preheat oven to 350 degrees F. Hollow out each mushroom cap, reserving scrapings. Brush caps, inside and out, with olive oil. Heat a skillet over medium-high heat. Cook and stir sausage, onion, and reserved mushroom scrapings in hot skillet until sausage is browned and cooked through, 4 to 6 minutes. Drain and discard grease; return sausage mixture to skillet. Stir 3 ounces Parmesan cheese, bread crumbs, garlic, and parsley into sausage mixture. Cook and stir until heated through, 3 to 5 minutes. Stuff each mushroom cap with sausage mixture and place on a baking sheet.
Bake stuffed mushrooms in the preheated oven for 12 minutes. Sprinkle remaining 1 ounce Parmesan cheese over mushrooms and bake until mushrooms are cooked through and cheese is melted and bubbling, about 3 minutes.