In a mixing bowl, add the flour, sugar and salt. Mix it together. Grate the cold butter into the bowl and using your hand, mix it around evenly. Pour the white vinegar and ice-cold water. Mix it together without kneading too much.

Drop the whole thing on a board and bring the dough together into a rectangular shape (it might take a little while but do not add any extra water). Fold the rectangle and then, spread it once again to form a rectangle. Fold again and repeat this process four to five times. Wrap the dough in a clear wrap and keep it in the refrigerator for 30 minutes. You can make the dough in advance and keep it in the refrigerator for a couple of weeks or freeze it for months!

When you are ready to prepare the galette, take it out of the refrigerator and leave it aside for 5 minutes. In the meantime, preheat the oven to 400 F and slice the heirloom tomatoes into thin slices. Slice the cherry tomatoes in halves. Also, make the whipped ricotta by whisking it with garlic, 1 egg, fresh thyme leaves and salt.

Place a parchment paper on a big cookie sheet.

Dust a little flour on your rolling pin and on the board. Start rolling the dough from center to outwards, rotate and roll again. Dust a little flour. Flip and roll again to ¼ inch thin.

Carefully lift the rolled dough and place it on the cookie sheet. Spread the whipped ricotta evenly, keeping 1 inch away from the edge.

Layer the sliced tomatoes on top of the ricotta. Now, gather the edges and carefully fold it over the tomatoes.

In a bowl, whisk 1 egg with 1-teaspoon water. Using a pastry brush, brush the edges. Spread little more fresh thyme leaves on the folded crust and on top of the tart. Sprinkle little salt on the tomatoes and drizzle the oil.

Place the cookie sheet in the middle rack of the oven and bake for 25 minutes or until the crust looks golden brown.