Preheat the oven to 400 degrees . In a medium skillet, heat the EVOO, 3 turns of the pan. Add the garlic and cook until softened.
In a bowl, beat the egg whites until stiff peaks form. In another bowl, beat the egg yolks and stir in the spinach and ricotta cheese; season with the salt, pepper and nutmeg. Fold in the egg whites. Pour the mixture into the hot skillet and cook over medium heat until just set around the edges, about 2 minutes.
Transfer the frittata to the oven and bake until golden and fluffy, about 15 minutes. Sprinkle the Parmigiano-Reggiano all over the top and bake for 2 minutes. Cut into wedges and serve immediately.