How to Make It
In a large pot of salted boiling water, cook the pasta until al dente. Drain.
Wipe out the pot; melt the butter in it. Add the scallions and garlic and cook over moderately high heat until softened, 2 minutes. Add the wine and simmer until reduced by half, 3 minutes. Stir in the mascarpone. Add the pasta and shrimp and cook, tossing, until the pasta is coated, 3 minutes. Stir in the spinach and season with salt and pepper. Serve hot.