To make the galette dough, add the flour and salt to a food processor and pulse together. Then add the butter pieces. Pulse until the dough looks shaggy and mostly combined.
3 cups all purpose flour, 1 tsp salt, 12 tbsp unsalted butter
Add the apple cider vinegar and pulse. Then add the ice water one tablespoon at a time, pulsing it as you go. You may need more or less ice water - when the dough forms into one large ball, stop adding water or else it will get too wet. Turn the dough out onto a counter and knead it about five times, just to form it into a nice disc. If it's really sticky, sprinkle some additional flour on the dough as you knead.Wrap the dough in plastic wrap and place it to chill in the fridge, for at least two hours or overnight. 7 tbsp ice cold water, 1 tbsp apple cider vinegar
Take your galette dough out of the fridge and let it sit for around 20 minutes. Meanwhile, preheat the oven to 400℉. On a cutting board, slice your heirloom tomato thinly. Place the tomatoes on a plate with a paper towel. Cover the tomatoes with another paper towel and gently tap it so it absorbs the excess water from the tomato. Let sit for 15 minutes.
1 large heirloom tomato
Grab your dough and lightly flour your work surface to prevent sticking. With your rolling pin, roll the dough into a large circle, at least 12 inches across and about an ⅛th inch thick. It doesn't have to be perfect.
Line a baking sheet with parchment paper. Transfer your dough to the baking sheet. In the center of your dough, place your mozzarella slices, leaving around a 2 inch border on all sides. Spoon on the pesto and smooth it out. Layer on the heirloom tomatoes, overlapping them to fully cover the pesto and cheese underneath.
4-5 slices mozzarella cheese, ¼ cup fresh pesto
Sprinkle the tomatoes with salt, pepper and red pepper flakes. Fold the edges of the dough over the edges of the tomatoes, leaving the center of the filling exposed.
salt and pepper, 1 pinch red pepper flakes
Brush the dough with the egg wash and while it's wet, sprinkle oregano on the crust. Place it in the oven and bake it for around 30-35 minutes, until the crust is golden brown. Allow to cool for 10-20 minutes before slicing to eat. Top with fresh basil.
1 egg, 1 pinch dried oregano, fresh basil