Line a large baking sheet with parchment paper. Lay the sheet of puff pastry on a cutting board and cut it into 6 equal rectangles. Lay each piece of puff pastry on the parchment-lined baking sheet, leaving a ½-inch space between each piece. Poke each piece with a fork a few times all over.

Sprinkle each piece of puff pastry with 1 ounce of shredded cheese, leaving a ¾-inch border around the edge, then place the baking sheet in the fridge while you prepare the tomatoes so that the puff pastry stays cold.

Generously salt each side of the tomato slices, lay them between two large paper towels on a large plate, and let them sit for 15 minutes. This will help draw out excess liquid from the tomatoes so that the tarts aren’t soggy. While the tomatoes sit, preheat the oven to 400ºF.

Take the baking sheet out of the fridge and top with the drained tomato slices and a sprinkle of fresh thyme. In a small bowl, whisk the egg with a fork and use a pastry brush to brush on the edges of each puff pastry piece. This will create a nice golden brown crust when baked.

Bake for 25-30 minutes until the pastry is deeply golden and crisp. Remove from the oven and season with freshly ground black pepper. If you’re serving these as appetizers, feel free to slice each piece in half diagonally. Serve warm.