Bring a largo pot of water to a boil, salt it, add the pasta and cook until just shy of al dente. Drain, reserving 1/2 cup pasta water.
In a large skillet, melt the butter over medium heat until foaming. Stir in the shallot and garlic for 2 to 3 minutes, then stir in the sherry. Stir in the tomatoes and season with salt and pepper. lightly crush the tomatoes with a potato masher. Bring the sauce to a bubble, lower the heat and simmer for 20 minutes.
Add the spinach to the sauce to wilt, then stir in the nutmeg. Add the pasta and reserved pasta water and turn with tongs to combine with the spinach and sauce. Serve in shallow bowls and top with the pecorino-romano.