The condiment Dijon mustard, with a little touch of onion and cooked with balsamic vinegar, deliciously enhances tomatoes and pairs very well with cheese.
It is so good that one tart is not enough for all four of us. We want to eat more!
1 pâte brisée or puff pastry
3 large tomatoes cut into ⅛ slices
3 medium onions finely sliced
1 cup or more Parmesan, Pecorino Romano, Comté, Gruyère, Cantal or fromage de chèvre, grated
2 tablespoons coarse Dijon mustard
1-2 tablespoons balsamic vinegar
1 teaspoon sugar
1 teaspoon Herbes de Provence or oregano
Salt and pepper
1. Unroll the pie crust and precisely fit it in a tart pan (11 inches). Poke the dough all over with a fork, then put the pie in the fridge.
2. Preheat the oven to 190C.
3. On a cutting board, slice the tomatoes (⅛ inches) and put them on a plate. Salt them lightly and set them aside. This step will help to remove some juice from the tomatoes so the crust will not be too soggy.
4. In a skillet, on medium-low heat, add 1 tablespoon olive oil, add the onions with salt, pepper and Herbes de Provence, and let them cook until soft. Add a splash (about 1-2 tbsp) of balsamic vinegar and sugar. Cook until the onions absorb all the vinegar and there is no juice. Set aside.
5. Take your tart pan from the fridge. Spread Dijon mustard evenly all over the bottom in a fine layer. Sprinkle evenly grated cheese on top. Scatter ¾ of the onions on the cheese. Take each tomato slice and shake them gently before placing them nicely on the tart.
6. Add the ¼ leftover onions on the top and sprinkle more grated cheese if you want. Drizzle some olive oil.
7. Cook for 25 to 30 minutes until the crust and the cheese are lightly golden.
Enjoy with a green salad on the side.
If you are worried about the sogginess of the dough, you can always add a few breadcrumbs or rolled oats before putting the tomatoes on the tart. It tastes good too!