Prepare the Puff Pastry:

1. Preheat the Oven: Preheat your oven to 400°F (200°C).
2. Prepare the Puff Pastry: Roll out the puff pastry sheet on a lightly floured surface. If using store-bought puff pastry, be sure to thaw it according to the package instructions. Cut the pastry into 8 equal squares or rounds, depending on your preferred shape.
3. Add an Egg Wash: Beat the egg and brush it lightly over the edges of each pastry square or round. This will give the tartlets a beautiful golden finish once baked.

Prepare the Tomato Filling:

4. Slice the Tomatoes: Thinly slice the tomatoes and place them on a paper towel to remove excess moisture. This will help prevent soggy tartlets.
5. Mix the Cheese: In a small bowl, combine the mozzarella and Parmesan cheeses. Stir in the fresh basil, oregano, salt, and pepper.

Assemble the Tartlets:

6. Layer the Ingredients: Place a spoonful of the cheese mixture in the center of each puff pastry square or round, spreading it evenly. Arrange the tomato slices on top of the cheese, slightly overlapping them.
7. Drizzle with Olive Oil: Lightly drizzle olive oil over the tomatoes and season with a pinch of salt and pepper.

Bake the Tartlets:

8. Bake: Place the tartlets on a baking sheet lined with parchment paper and bake in the preheated oven for 15-20 minutes, or until the pastry is golden brown and puffed up, and the tomatoes are tender.
9. Garnish and Serve: Remove the tartlets from the oven and let them cool slightly. Garnish with fresh basil leaves before serving, if desired.