Pasta with Lemon and Mascarpone Sauce

3 tablespoons unsalted butter, at room temperature
1/3 cup mascarpone cheese, at room temperature
grated zest of 1 medium lemon
2 tablespoons fresh lemon juice
? teaspoon salt, or to taste
freshly ground black pepper
1/4 cup freshly grated Parmesan

Combine all ingredients in heatproof bowl and place over pasta water while it comes to a boil. Toss with cooked pasta.
Recommended pasta: 8 ounces penne or shells.

from No Cook Pasta Sauce.