Combine the ricotta, egg yolks, spinach, Parmigiano, all-purpose flour, panko, and nutmeg. Let the dough rest for 10 minutes.
Using a cookie scoop, roll the dough into balls a little smaller than golf balls. Coat a baking sheet liberally with semolina flour, place the gnudi on top of the semolina, then sprinkle more semolina on top. Refrigerate, uncovered, for 12 hours or overnight befo