Step 1

Simmer the broth: In a 2-quart pot or saucepan over medium heat, bring the broth to a simmer.

Step 2

Whisk the eggs: Whisk together the eggs and 3/4 cup of the Parmigiano cheese until well combined, save the remaining 1/4 cup of cheese to sprinkle on top of the soup just before serving. If using nutmeg, grate in a small amount—about a pinch worth—and whisk to combine. Set aside

Step 3

Add the spinach and lemon zest to the broth: Stir the chopped spinach into the simmering chicken broth and cook until the spinach is heated through and the broth is simmering once more, about 5 minutes. Don’t be alarmed at the amount of spinach. It will wilt down to only about 1 cup in the soup. Stir in the lemon zest, if using.

Step 4

Add the eggs: Slowly pour the egg mixture into the soup. Gently stir once or twice with a wooden spoon or a fork. Simmer, uncovered, for a couple of minutes without stirring, until the eggs are fluffy and set. They will float on top of the broth in a soft mass. Gently break up the eggs into soft clumps.

Step 5

Serve: Ladle the soup into warmed bowls and sprinkle the remaining Parmigiano-Reggiano on top. Serve hot.