Mushrooms are sautéed and cooked down in marsala for the base of this creamy pasta sauce.
Heat a large pot of boiling water for pasta.
Heat a large skillet over medium-high heat with EVOO, 2 turns of the pan, melt butter into oil and when it foams, add the mushrooms, brown 15 minutes, stirring frequently, add shallots, garlic, rosemary, salt and pepper, stir 2-3 minutes more. Add the Marsala wine, about ½ cup, and swirl a minute, add bone broth or stock and reduce heat to low bubble, simmer.
Salt boiling water and cook pasta about 7 minutes, reserve ½ cup of starchy water and drain pasta.
Stir the mascarpone into sauce and turn off heat then add Dijon mustard. Toss spaghetti with sauce and cheese, taste to adjust seasoning. Top with parsley, and nuts if using.