Thaw Puff Pastry: Begin by removing the frozen puff pastry from the freezer and placing it in the refrigerator for at least 3 hours or overnight to thaw. If you're short on time, leave it out at room temperature for about 30 minutes instead.

Prepare the Dough: On a lightly floured surface, carefully roll each sheet of puff pastry to a thickness of about 1/16 inch. Use a fork to prick the surface evenly to prevent the dough from puffing up too much during baking.

Cut the Circles: Using a biscuit cutter, cut out approximately 30 circles from the rolled pastry. Ensure the circles are slightly larger than your tomato slices.

Arrange on Baking Sheet: Line a baking sheet with parchment paper and place the pastry circles on top, spacing them about an inch apart.

Add Cheese and Tomatoes: Top each pastry circle with about 1 teaspoon of grated Gruyère cheese, followed by a slice of tomato or halved cherry tomatoes.

Season for Flavor: Sprinkle kosher salt, freshly ground black pepper, and chopped thyme generously over each tart.

Bake to Perfection: Preheat your oven to 400°F (200°C) and bake for 20 to 25 minutes.

Cool and Serve: Remove from the oven and allow cooling for a few minutes. Serve warm or at room temperature.