Gorgonzola Mushroom Boule

Name: Gorgonzola Mushroom Boule
Ingredients: 4 tablespoons unsalted butter; 2 tablespoons olive oil; 1/2 Spanish onion; 8 ounces white mushrooms, sliced 1/4-inch thick; 8 ounces portobello mushrooms, stemmed and sliced 1/4-inch thick; 4 sprigs fresh rosemary; 1 teaspoon kosher salt; 1/2 teaspoon freshly ground black pepper; 2 tablespoons dry white wine; 4 ounces gorgonzola, crumbled; 1 cup heavy cream; 1 sourdough bread boule, hollowed out; Fresh rosemary sprigs, for garnish; 1 baguette, sliced, for serving