Prepare the Spinach: Heat olive oil in a pan over medium heat. Sauté the garlic until fragrant, then add spinach and cook until wilted. Remove excess moisture by squeezing with a kitchen towel.
Make the Filling: In a bowl, mix the spinach, ricotta, mozzarella, Parmesan, egg, salt, and black pepper until well combined.
Prepare the Puff Pastry: Roll out the puff pastry on a lightly floured surface. Spread the spinach filling evenly, leaving a small border.
Roll & Cut: Roll the pastry tightly into a log and slice into 6–8 pieces.
Apply Egg Wash: Brush the tops with the beaten egg and milk mixture. Sprinkle with sesame seeds if desired.
Bake: Preheat the oven to 375°F (190°C). Arrange the rolls on a lined baking sheet and bake for 20–25 minutes, or until golden and flaky.
Cool & Serve: Let the rolls cool for a few minutes before serving warm.