To make the crust, add flour and salt to the bowl of a food processor. Pulse a few times to combine.
1 ½ cups all purpose flour, ½ teaspoon kosher salt
Add cubed butter. Pulse again until it forms a crumb.
10 tablespoons unsalted butter
Pour in water and apple cider vinegar. Pulse just until it forms a thick dough.
3 tablespoons ice water, 1 teaspoon apple cider vinegar
Lightly flour a clean surface and a rolling pin.
Form the dough into a disc and roll the dough into a circle over the floured surface until it’s about ⅛ of an inch thick and about 12 inches wide. The thinner, the better.
Carefully use the rolling pin to help transfer the dough to a parchment-lined baking sheet.
Place baking sheet in the fridge and let dough chill for at least 1 hour.
Towards the end of the chilling time, slice up the tomatoes and place them in a bowl with ½ teaspoon kosher salt.
2-3 heirloom tomatoes
Gently mix with your hands to cover in the salt.
Let tomatoes sit for about 10-15 minutes so the salt can draw out some of the excess moisture.
Preheat your oven to 400 degrees F.
Remove dough from the fridge. Let sit at room temperature for about 5 minutes so the dough softens just enough to be able to fold it without cracking.
Spread the Boursin cheese in the center of the dough, leaving about an inch of space around the edges.
5.3 ounce package garlic herb Boursin cheese
Drain the tomatoes and set them on paper towels to absorb any remaining moisture. Arrange the tomatoes on top of the cheese.
Sprinkle parmesan cheese over top.
2 tablespoons fresh grated parmesan cheese
Carefully fold the edges of the dough on top of the edges of tomatoes, leaving the center filling exposed.
In a small bowl, whisk together egg and water.
1 large egg, 1 tablespoon water
Using a pastry brush, brush the egg wash on top of the folded dough.
Bake for 35-40 minutes, or until the crust is light golden brown.
Allow to cool for at least 10 minutes on the baking sheet before transferring to a serving plate.
Garnish with fresh chives, basil, or oregano. Sprinkle flaky sea salt over top.
Notes
Butter: You can substitute salted butter for the unsalted butter and omit the salt.
Salt: If you don't have kosher salt or sea salt, you can use half the amount of table salt.
Heirloom tomatoes: Heirloom tomatoes will give you good flavor in this dish. If you don't want to use heirloom variety tomatoes, use your favorite flavorful, beefy tomatoes.
Boursin: The cheese is going to give the galette richness and flavor. Plain Boursin cheese won't give the galette the same flavor.