Mix ricotta, egg, egg yolk, pepper, Parmesan, and teaspoons salt in a large bowl until well combined. Add plain flour; stir just until combined and mixture forms a ball (mixture will be soft and moist with some bits of ricotta remaining; add more flour by the tablespoonful if it still feels wet).
Dust a rimmed baking sheet generously with the polenta. Using 2 large soup spoons, shape heaping tablespoonfuls of dough into ovals; place on baking sheet and dust with more flour (you should have about 16).
Cook gnudi in a large pan of boiling salted water, stirring occasionally, until cooked through and tender, 5-6 minutes (gnudi will quickly float to surface; continue cooking or gnudi will be gummy in the center).
Using a slotted spoon, divide gnudi among bowls. Serve with pesto or butter and sage, and more Parmesan.