1/2 cup shredded Pecorino Romano or Parmesan cheese
1 garlic clove, grated
1 teaspoon fresh thyme leaves
Instructions
In a medium bowl, mix the flour, sugar, kosher salt, and baking powder. Slice the butter into small pieces, then use a pastry blender or fork to cut it into the flour mixture until mostly incorporated and a pebbly texture forms (with pea-sized or smaller pieces).
Sprinkle 4 tablespoons of the cool water over the flour, mixing gradually with a fork until the flour is mostly incorporated. Add the additional 1 to 2 tablespoons of water until all the flour is incorporated, kneading with your fingers until the dough comes together. (Resist the urge to add more water; it should come together!) Form the dough into a ball and flatten into a thick disk. Wrap it in plastic or place it in a covered container and chill the dough for 1 hour. (To make in advance, you can refrigerate the dough up to 3 days; allow to sit at room temperature 30 minutes before rolling. Or, wrap in plastic wrap or aluminum foil and freeze up to 3 months, then defrost overnight in the refrigerator before rolling.)
Preheat the oven to 400 degrees Fahrenheit.
Slice the tomatoes and place them on a cutting board or paper towel. Sprinkle them with 1/2 teaspoon kosher salt and fresh ground pepper, divided between the slices. Allow them to sit while you prepare the rest of the filling (about 15 to 20 minutes).
Mix the ricotta, Pecorino Romano or Parmesan cheese, grated garlic, 1/2 teaspoon salt, and fresh ground pepper.
On a floured surface, roll the dough into an even 12” circle, leaving the edges rough (if needed, move the dough around and add a bit more flour underneath to keep it from sticking). Carefully transfer the dough to a sheet of parchment paper on a rimmed baking sheet.
Gently spread the cheese mixture on the dough, leaving at least 2 inches of dough around the outside edge. Place the tomato slices on top, shaking any liquid off of each slice before placing it onto the galette. As necessary, slice tomatoes in half to fill the entire circle of cheese filling (see the photos above). Fold in the outside edges of the dough over the filling to form an approximately 2-inch crust, overlapping the folds as shown in the photos.
Whisk the egg and use a pastry brush to brush it onto the crust.
Bake the galette for 25 to 30 minutes until the crust is golden brown. Remove from the oven and transfer the parchment paper to a baking rack to cool. Cool to room temperature (about 1 hour) before topping with thyme leaves. Slice into pieces and serve. Store leftovers for up to 3 days refrigerated; bring to room temperature or warm in the oven before serving.