Bring a pot of water to a boil. In a large nonstick skillet, warm oil over medium-high heat. Add leeks and shallots and sprinkle with 1/2 tsp. each salt and pepper; sauté until tender, 5 minutes. Add mushrooms; sauté until cooked down, 7 minutes. Pour in wine; simmer until reduced by half, 2 minutes. Remove skillet from heat.
Add 1 tsp. salt and pasta to boiling water. Stir and cook until pasta is al dente, 9 minutes or according to package directions. Reserve 1/2 cup cooking water; drain pasta.
Add pasta, cooking water, broth, mascarpone and parsley to skillet. Cook over medium-low heat, stirring, until liquid has reduced and pasta is well coated, 3 minutes. Season with additional salt and pepper, if desired.