In a heavy, wide, deep skillet, heat the butter and olive oil over medium heat until hot.
Add the shallots and garlic and sauté for 2-3 minutes until softened and fragrant.
Step 2
Turn the heat to medium-high, add the porcinis, and cook for a few minutes, allowing most of the water to cook out. Season lightly with salt and pepper.
Step 3
Add the remaining mushrooms and stir to coat. Leave undisturbed for about 3 minutes, or until well-browned.
Season once again with salt and pepper, stir, and allow the mushrooms to finish cooking until they are browned and the water has cooked out.
Step 4
Add the wine and stir, scraping up any fond that has collected at the bottom of the pan. Allow the wine to reduce, add the balsamic vinegar, and stir well to combine.
Add the heavy cream, bring to a simmer, and reduce the heat to medium-low. Allow to simmer for several minutes, concentrating the flavor. Whisk in a little of the reserved water from cooking the pasta, ¼ to ½ cup, which improves the texture of the sauce.
Step 6
Stir in the cheese with a wooden spoon until melted and combined. Add the pasta, stir to combine, and allow to gently simmer for a minute or two. Taste and adjust the seasoning if necessary.
Step 7
Divide between serving bowls. Garnish with fresh parsley and additional cheese.