In a large bowl, combine the drained ricotta, finely chopped spinach, grated Parmesan cheese, egg yolks, salt, black pepper, and ground nutmeg. Mix until well incorporated.

Gently fold the all-purpose flour into the ricotta mixture until a soft dough forms. Do not overmix.

Spread the semolina flour onto a rimmed baking sheet. Scoop 1-inch mounds of the ricotta dough and gently roll them into balls using your hands.

Place the rolled gnudi onto the semolina-coated baking sheet, rolling them around to ensure they are completely coated in semolina flour.

Transfer the baking sheet to the refrigerator. Chill the gnudi uncovered for at least 1 hour to allow them to firm up.

Bring a large pot of heavily salted water to a gentle boil.

While the water heats, melt the unsalted butter in a large skillet over medium heat. Cook the butter for 3-4 minutes until it turns golden brown and gives off a nutty aroma.

Add the fresh sage leaves to the browned butter, cook for 30 seconds until crispy, then remove the skillet from the heat.

Carefully drop the chilled gnudi into the gently boiling water in small batches. Cook until they float to the surface, then allow them to simmer for 1 to 2 additional minutes.

Use a slotted spoon to transfer the cooked gnudi directly into the warm brown butter and sage sauce. Toss gently to coat.

Serve immediately with an extra sprinkle of grated Parmesan cheese.