Arrange tomato slices over a wire rack in a baking sheet. Sprinkle with kosher salt and set aside for at least 30 minutes to drain. An optional additional step is to move them to paper towels to further absorb any moisture or they can be blotted before assembling the galette.
Preheat oven to 400 degrees Fahrenheit with a rack positioned in the center. Line a half baking sheet with parchment paper.
Roll out the puff pastry on a lightly floured surface until it’s roughly 13x16 inches. Loosely roll the dough around the rolling pin and carefully transfer it to the prepared baking sheet, laying it out completely flat.
Sprinkle the cheese evenly over the center of the dough, leaving a 2-inch border along each edge. Top with garlic, half of the thyme, oregano, sea salt, and pepper. Layer the tomatoes on top and add the rest of the thyme.
Fold the edges over the filling, crimping and overlapping as needed. Brush the dough with egg.
Bake the galette until the crust is golden brown and cooked through, about 25-40 minutes depending on your oven.
Let cool at least 10 minutes. Garnish with fresh basil and/or additional thyme leaves.
Serve warm and enjoy!