Preheat oven to 400 F. Line a baking sheet with parchment paper; set aside.
Roll out puff pastry sheets on a lightly floured surface. Use a 3-inch cookie cutter to cut 9 circles out of each sheet of dough. You should have 18 circles.
Baste the tops of each circle with egg mixture.
Lay a few tomato slices on 9 of the dough circles. Sprinkle with salt and pepper, and drizzle with balsamic reduction.
Place the remaining nine circles of dough on top of the others, covering the tomatoes. Use a fork to pinch the edges together. (Egg washed sides should be pressed together)
Lay a slice of tomato on top of each circle, and transfer to prepared baking sheet. Sprinkle with salt and pepper.
Bake 15-18 minutes until puff pastry is puffy and browned. Remove from heat.
Drizzle with balsamic reduction and garnish with fresh basil.