Place four cutlets on a flat work surface. In a small bowl, mix the ricotta with lemon zest and nutmeg. Dollop 2 tablespoons in the center of one side of each cutlet; close the cutlet like a book, then press down on the edges and flatten a bit to seal in the cheese.
Season the flour with salt and pepper and dredge the stuffed cutlets lightly. Top each cutlet with sage and then with prosciutto slices.
Pre-heat an oven to175°F and warm a platter.
Heat a large skillet over medium-high heat with oil, two turns of the pan. Cook two cutlets, ham-side down first until browned and cooked through, 6-7 minutes, turning once. Transfer to a platter, then add another turn of oil and repeat. Once the cutlets are cooked, add the wine to the pan and scrape the drippings from the bottom of the pan. Add the lemon juice and butter to the pan, then swirl and spoon over meat. Serve immediately.