Adapted from Smitten Kitchen
1 1/4 cups all-purpose flour, chilled in the freezer for 30 minutes
1/4 tsp salt
8 Tbsp cold unsalted butter, cut into pieces and chill again
1/4 cup sour cream
2 tsp fresh lemon juice
1/4 cup ice water
1 large or 2 small zucchinis, sliced into 1/4 inch thick rounds
1 Tbsp plus 1 teaspoon olive oil
1 medium garlic clove, minced (about 1 teaspoon)
1/2 cup ricotta cheese
1/2 cup (about 1 ounce) grated Parmesan cheese
1/4 cup (1 ounce) shredded mozzarella
1 Tbsp slivered basil leaves
1 egg yolk beaten with 1 teaspoon water
For Crust: Combine flour and salt in a large bowl. Cut in butter cubes with a pastry blender until mixture becomes a course meal.
Whisk together sour cream, lemon juice and water in a small bowl. Poor over the flour butter mixture. Gently mix with hands and form into a ball. Avoid over working the dough. Wrap in plastic and place in the refrigerator for at least one hour.
For filling: Place zucchini slices in a single layer on paper towels. Sprinkle with salt and allow to drain for 30 minutes. Blot zucchini with paper towels to dry. Whisk together olive oil and garlic and a small bowl. In a separate bowl, combine ricotta, parmesan, mozzarella and 1 tsp of garlic and olive oil mixture. Add salt and pepper to taste.
Heat oven to 400°F. Remove dough from fridge and place on a lightly floured surface. Roll with a floured rolling pin into a disc 12 inches in diameter. Place crust on a baking sheet lined with parchment paper. Spread cheese mixture over dough, leaving room for a 2 inch boarder. Arrange zucchini in an attractive shingle pattern in concentric circles over the cheese. Drizzle remaining garlic olive oil over the top and brush to coat. Fold up crust and pleat to fit. Brush crust edges with egg yolk glaze.
Place gallette in oven and bake for 30 to 40 minutes. Remove from oven when zucchini is slightly wilted and edges of galette are golden brown. Sprinkle basil over top of hot galette and allow to wilt. Transfer galette to serving platter. Slice into wedges and serve hot, warm or at room temperature.