Prepare crust. In food processor, combine flour, cheese and salt. Pulse a few times to mix. Add butter. Pulse until butter is the size of peas. Turn food processor on low, add water and vinegar. Keep processor on until dough just begins to come together. Remove from bowl onto a floured work surface. Knead dough twice and pat together to form a flat disk about 1-inch thick. Wrap in plastic wrap and refrigerate 2 hours or more.

Cut zucchinis into quarters lengthwise, then cut into 1.5-2-inch pieces crosswise. Place in colander and toss with 2 teaspoons of the salt. Set aside to drain for 30 minutes. Remove to paper towel to dry.

Meanwhile, prepare ricotta. In a small bowl, mix together ricotta, Grana Padano, lemon zest and ¼ teaspoon of the salt.

To assemble, position rack in middle of oven and preheat to 400 degrees. Line a rimless baking sheet with parchment paper. On a floured work surface, roll out dough to a 15- inch circle – it does not need to be perfectly round or have smooth edges. Roll the dough onto your rolling pin and transfer to baking sheet. With an offset spatula, spread ricotta mixture over dough, leave 1-inch of naked dough around the edge. Pile the zucchini onto the dough, slightly mounding it in the center and leaving a 2-inch border around the edge. Fold the rim of the dough up and over the edge of the filling, overlapping the dough as you go around and pleat the dough. Brush dough with egg. Bake until pastry is golden brown, about 1 hour.

Yields 6 slices.