Prepare the puff pastry. Preheat your oven to 400°F (200°C). Line two baking sheets with parchment paper. Unfold the puff pastry sheet(s) and place them on a lightly floured surface. Gently roll out each sheet to smooth creases and slightly increase the size. Cut each sheet into 6 equal pieces, making 12 total rectangles. Transfer the puff pastry rectangles to the prepared baking sheets.

Prep the pumpkin and apples. Slice the squash in half and scoop out the seeds. Thinly slice into 1/4 inch thick pieces. Slice the apple into pieces with similar thickness, avoiding the seeds and stem. In a large bowl, combine the melted butter, garlic powder, salt, and fresh thyme. Add the sliced pumpkin and apples, tossing gently to coat evenly.

Assemble and bake the tartlets. Arrange the coated pumpkin and apple slices on top of each puff pastry rectangle. Sprinkle with some of the grated Parmesan cheese. Bake in the preheated oven for 25-30 minutes, rotating the baking sheets halfway through, until the pastry is puffed and golden and the pumpkin and apples are tender.

Make the balsamic glaze. While the tarts bake, in a small saucepan, combine the balsamic vinegar and maple syrup. Place over medium heat and bring to a gentle boil. Reduce the heat to low and simmer, stirring occasionally, until the liquid has reduced by about half and reaches a syrupy consistency, about 5- 10 minutes.

Finish with balsamic glaze. Once the tartlets are out of the oven, drizzle with the maple balsamic glaze, sprinkle with reamaining cheese, grate over some black pepper, and garnish with additional thyme leaves.