For the pastry: Place all-purpose flour, whole wheat flour and salt in a food processor. Turn the processor on until blended. Add the butter, and process just until butter is crumbly. Add eggs and 2 tablespoons of ice water, and pulse until mixture just begins to come together. If needed, add more water (1 tablespoon at a time). NOTE: You want to be able to see some small pieces of butter in the dough.
Remove dough from the food processor, and divide in half. Roll dough to about ½ inch thick, and then fold top ⅓ over the dough from top to bottom.
Next fold the bottom ⅓ up, and gently press.
Repeat this process, going from left to right.
Finally, fold from right to left. This process helps create flaky layers in the dough. Repeat the process with the second piece of dough, wrap in plastic wrap, and refrigerate for at least 1 hour. NOTE: The dough can be made ahead and refrigerated for up to 2 days.
For the tart: Thinly slice tomatoes and lay on a sheet pan lined with paper towels or a dish towel. Sprinkle evenly with coarse Kosher salt. Add a second layer of towels and tomatoes if need be.
For the filling: Mix together the ricotta cheese, mozzarella cheese, lemon zest and juice, basil and salt and pepper.
Preheat the oven to 400°F.
Remove dough from the refrigerator, and roll to a 12-inch circle, about ⅛ - ¼ inch thick. Place the dough on a parchment lined sheet pan. Spread ½ of the ricotta mixture on each piece of dough, leaving a 2-inch gap between the filling and edge of the dough.
Layer tomatoes in a single layer on the filling mixture, just slightly overlapping them. Gently fold the dough up over the tomatoes, and allow the dough to fold over itself, until you have folded all the dough up. Gently brush the dough with the egg.
Place the tarts in the oven for 30-35 minutes, rotating them halfway through baking. Remove tarts from the oven, and let cool for 15 minutes before slicing into 8 even slices. I love to serve this with a simple greens salad for a light vegetarian meal!