Marie’s French Tomato Tart

1 recipe French pastry dough
1 Tbsp Dijon mustard
1 cup grated cheese Gruyère, Emmenthal, or Comté are best, but your favorite hard cheese will do
3-4 tomatoes depending on size, cored and sliced into ¼-inch rounds

Heat the oven to 400° F. Line a large rimmed sheet pan with parchment paper.
On a lightly floured surface, roll out the pastry to 1/8-inch thick. You should have a rectangle measuring about 9 x 12 inches. Rough edges are totally fine. Roll it carefully onto a rolling pin and unroll onto prepared sheet pan. Using a fork, poke holes all over the pastry surface so it doesn’t puff up.
Spread the Dijon over the pastry shell, leaving a 1-inch border around the edges, then sprinkle the cheese evenly over top. Lay tomato rounds over the cheese layer so they touch but do not overlap. Season with sea salt and pepper.
Bake until the cheese is bubbly and the crust is brown, 25–35 minutes.
Let rest for 5 minutes before slicing and serving.