Preheat the oven to 400°F (200°C), lining a baking sheet with parchment paper.

Sauté finely minced garlic and onion in a drizzle of olive oil over medium heat until translucent and fragrant, about 3 minutes.

Mix wilted spinach, cream cheese, mozzarella, Parmesan, salt, and pepper in a medium bowl until smooth and evenly combined.

Roll pastry sheets on a lightly floured surface to smooth seams and cut into rectangles (about 4x6 inches each).

Fill each rectangle with a generous spoonful of spinach-cheese mixture, leaving a ½-inch border around edges.

Fold one half of each rectangle over the filling, pressing edges with a fork to crimp and seal; brush tops with egg wash.

Bake puff pastry for 18–20 minutes until golden brown and the filling is hot and bubbly.