In a large bowl, mix the flour and salt. Add the butter and work it in with your hands until it looks like coarse crumbs. In another bowl, whisk together the sour cream, lemon juice, and ice water. Add this mixture to the flour mixture and mix until large lumps form. Pat the lumps into a ball, wrap in plastic wrap, and refrigerate for 1 hour.

Spread the zucchini slices on paper towels to remove excess moisture. Sprinkle with salt and let them sit for 30 minutes, then pat dry with a clean towel.

In a medium bowl, mix the ricotta, Parmesan, mozzarella, garlic, and basil until well combined.

Preheat the oven to 400°F.

On a floured surface, roll out the chilled dough into a 12-inch round. Place it on a baking sheet lined with parchment paper. Spread the ricotta mixture over the dough, leaving a 2-inch border. Arrange the zucchini slices on top of the ricotta in circles, starting from the outside edge. Drizzle with olive oil. Fold the border over the filling, pleating the edge as needed. Brush the crust with egg yolk.

Bake in the preheated oven for 35-45 minutes, until the pastry is golden brown and the zucchini is slightly charred. Remove from the oven and let it sit for 5 minutes before transferring to a serving plate. Slice and enjoy!