To make the galette dough: Mix together the flour and salt in a large mixing bowl. Using a pastry cutter or your fingers, cut in the cubes of butter until they are crumbly and pea-sized.
Mix in the ice-cold water one tablespoon at a time, stirring with a wooden spoon until a cohesive ball of dough forms. The dough will still be slightly crumbly, that's okay. Wrap tightly in plastic wrap and let rest in the fridge for 30 minutes.
Preheat the oven to 425°F.
Meanwhile, prep the filling. Roughly chop the garlic. Heat the olive oil over medium heat in a large skillet. Add the garlic, cherry tomatoes, balsamic vinegar, thyme, and salt. Saute just until the cherry tomatoes burst, about 8-10 minutes, stirring frequently. Set aside.
On a lightly floured surface, roll out the pastry dough into a 12-inch circle. Place on a parchment paper lined sheet pan or on a preheated pizza stone.
Pour the cherry tomato filling into the center of the galette, leaving about 2 inches of a border. Fold the border in over just the edges of the cherry tomatoes (see pictures for how it should look).
Bake for 25-30 minutes at 425F on the middle oven rack, until the galette is golden brown. Remove the galette from the oven and allow to cool for 10 to 15 minutes before cutting.
Notes
Vegan option: Just use an equal amount of vegan butter to make this galette dairy-free.
Keep ingredients cold: Just like with biscuits, I recommend cubing and freezing butter for at least 10 minutes before adding it to the dough. This keeps the butter from melting prematurely.
You can use any variety of cherry tomatoes or grape tomatoes.
Leftovers: Leftover galette keeps for 3 to 4 days. The easiest way to reheat the leftover galette is by heating it in a skillet over medium heat.