In a large skillet, heat olive oil to medium heat. Add spinach; cook until just wilted, 2-3 minutes. Let cool. Use your hands to squeeze the spinach juice back into the skillet. Transfer spinach to a cutting board; finely chop. Set aside.

Bring a large pot of salted water to a boil.

In a large bowl, mix together ricotta, spinach and egg until well-blended. Add Parmesan, garlic, salt, pepper and nutmeg, if desired; mix until thoroughly combined. Add flour; stir gently until a moist mixture forms.

Place a few tablespoons of flour on a plate. Using a teaspoon, scoop 1-in. balls of dough; roll in between the palm of your hands. Roll in the flour until lightly coated; set aside. Repeat with remaining dough.

Place skillet with spinach liquid back on the stovetop. Add tomato sauce; heat to medium.

Add dumplings to the water; lower to a gentle simmer. When the dumplings rise to the top, cook for 2 minutes. Scoop them out with a slotted spoon; transfer to the tomato sauce. Serve in bowls topped with additional Parmesan cheese.