Heat olive oil in a skillet over medium heat. Add diced onion and cook until translucent, about 3-4 minutes.

Add minced garlic to the skillet and sauté for an additional 1 minute.

Add chopped spinach to the skillet and cook until wilted, about 4-5 minutes. Remove from heat and let cool slightly.

In a mixing bowl, combine the cooked spinach mixture, ricotta cheese, shredded mozzarella, ground nutmeg, salt, and pepper. Mix well to create the filling.

Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.

Place an empanada dough disc on a flat surface and add about 1-2 tablespoons of the spinach filling in the center. Fold the dough over to create a half-moon shape and press the edges to seal. Use a fork to crimp the edges for added security.

Repeat the process with the remaining dough discs and filling.

Brush the top of each empanada with beaten egg to give them a golden finish.

Place the empanadas on the prepared baking sheet and bake in the preheated oven for 20-25 minutes, or until golden brown.

Remove from the oven and let cool for a few minutes before serving.