Spicy Italian Stuffed Mushrooms

Name: Spicy Italian Stuffed Mushrooms
Ingredients: 24 large white or cremini mushrooms, wiped clean, stems finely chopped for the filling; 2 tablespoons extra-virgin olive oil; Kosher salt; 1/4 cup extra-virgin olive oil; 1/2 cup finely chopped celery; 1/2 cup finely chopped onion; Kosher salt and freshly ground black pepper; 1/2 cup grated mozzarella; 1/2 cup cooked, crumbled spicy Italian sausage; 2 tablespoons finely chopped fresh basil, plus more for garnish (optional); 2 tablespoons finely chopped pepperoncini; 1 cup coarse fresh white breadcrumbs