If using fresh spinach, strip leaves from stems, soak and rinse, cook, then squeeze gently dry. Chop fine. If using thawed frozen spinach, squeeze dry, chop fine, and set aside.
Melt half the butter in a saute pan over medium-high heat. When the foam begins to subside, add the ham, turn it a few times, then add spinach and liberal pinches of salt. Saute over lively heat about 2 minutes, turning frequently.
Take off heat and mix in freshly grated nutmeg, no more than 1/8 teaspoon.
Toss the pasta with the pan contents, plus the ricotta, the remaining butter, and the grated Parmigiano-Reggiano. Serve at once, with more cheese on the side.
