Toast the Breadcrumbs: In a large, dry non-stick pan over medium heat, add the breadcrumbs. Shake and stir often until the breadcrumbs start to brown. You can brown them lightly or to a deep golden brown, but do not burn them. Remove the breadcrumbs and set aside for the garnish. Wipe down the pan.
½ cup panko bread crumbs
Crisp the Prosciutto: To the large, dry non-stick pan over medium heat, add the prosciutto slices and cook for about 15 seconds until the white fat turns clear and the prosciutto crisps up a bit. Remove the prosciutto and chop it finely, set aside.
3 slices prosciutto
Cook the Mushrooms and Onion: In the same pan, add the olive oil over medium heat. Add the onion and cook until it just starts to brown. Add the garlic and cook for 20 seconds. Add the butter until melted, then add the mushrooms, chopped cooked prosciutto (reserve some for garnish if desired), rosemary, kosher salt, black pepper, and parsley. The butter will be absorbed quickly by the mushrooms. Continue to cook until the mushrooms release some juices - about 5 minutes.
1 Tablespoon olive oil, ½ small onion, 1 large garlic clove, 3 Tablespoons unsalted butter, 1 ½ ounces dried porcini mushrooms, 5 ounces shiitake mushrooms, 1 teaspoon finely chopped rosemary, 1 teaspoon kosher salt, ½ teaspoon black pepper, 1 teaspoon finely chopped parsley
Finish the Filling: Once the mushrooms have cooked, add the red wine and sprinkle with the flour. Cook for another few minutes. The mushroom mixture should be thick. Add the cream and stir, and cook for a few more minutes. Remove from the heat and stir in the balsamic vinegar and the parmesan cheese. Set aside to cool.
½ cup dry red wine, 2 teaspoons all-purpose flour, 2 Tablespoons heavy cream, 3-5 drops balsamic vinegar, 3 Tablespoons grated Parmesan cheese