Step 1

In a large bowl, combine the flour and salt. Add in the butter and, using your hands, work it in until the mixture resembles coarse meal. In a smaller bowl, whisk together the sour cream, lemon juice, and water and add this to the flour mixture. Mix with your fingers until large lumps form. Pat the lumps into a ball and wrap with plastic wrap. Refrigerate for 1 hour.

Step 2

Lay the zucchini slices out on paper towels to absorb excess moisture. Sprinkle with the salt and let stand for 30 minutes, then pat dry with a clean towel.

Step 3

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

Step 4

Preheat your oven to 400°F (200°C).

Step 5

On a floured work surface, roll out the chilled dough into a 12-inch round. Transfer to a baking sheet lined with parchment paper. Spread the ricotta mixture evenly over the dough, leaving a 2-inch border. Lay the zucchini slices on top of the ricotta in concentric circles, starting at the outer edge. Drizzle with the tablespoon of olive oil. Fold the border over the filling, pleating the edge to make it fit. Brush crust with egg yolk.

Step 6

Bake the galette in the preheated oven for about 35-45 minutes, or until the pastry is nicely golden brown and the zucchini is very slightly charred. Remove from the oven and let stand for 5 minutes, then slide the galette onto a serving plate. Slice and serve!