Preheat the Oven: Begin by preheating your oven to 400°F (200°C).

Prepare the Puff Pastry: On a lightly floured surface, roll out the puff pastry sheet to fit a tart pan (around 9-10 inches). Trim off any excess and press the pastry into the pan. Prick the bottom with a fork to prevent bubbling.

Layer the Cheese: Sprinkle the shredded mozzarella cheese evenly over the bottom of the pastry. Then, add the crumbled feta on top of the mozzarella.

Arrange the Tomatoes: Lay the sliced tomatoes in an overlapping circular pattern over the cheese layers. Make sure to leave some space between the slices to allow for even cooking.

Season the Tart: Drizzle the olive oil over the top of the tomatoes. Season with salt, freshly cracked black pepper, and a sprinkle of dried basil if desired.

Add Fresh Basil: Tear the fresh basil leaves and scatter them over the tomatoes. They will add lovely flavor as they cook.

Egg Wash: Brush the edges of the puff pastry with the beaten egg to give it a golden finish as it bakes.

Bake the Tart: Place the tart in the preheated oven and bake for 20-25 minutes, or until the pastry is puffed and golden brown, and the tomatoes are tender.

Add Balsamic Reduction: Once out of the oven, drizzle the balsamic reduction (if using) over the tart for a sweet tangy finish.

Serve: Allow the tart to cool slightly before slicing. Serve warm or at room temperature, garnished with additional black pepper if desired.