Make the dough: In the bowl of a mixer, blend the flour, sugar, and lemon zest at low speed. Add the butter and continue blending at low speed until the mixture is coarse and sandy-looking. Add the egg mixture and blend just until the mixture comes together. Form into a ball, wrap with plastic wrap, and refrigerate at least 1 hour.
Preheat the oven to 375 degrees F.
On a floured surface, roll the dough out to a rough circle, about 14 to 15 inches in diameter. Transfer it to a baking sheet lined with parchment paper. All around the edge of the crust, fold in the outer half-inch to form a rough, "rustic" edge to the tart.
Filling: In a small mixing bowl whisk together the ricotta, egg white, sugar, and lemon zest. Using a rubber spatula, gently spread the ricotta filling over the bottom of the tart. Then arrange the tomato halves in concentric circles, cut side up, over the ricotta. Drizzle the honey over.
With a pastry brush, brush the tart edge with milk. Sprinkle it with coarse sugar. Bake until fruit is tender and the underside of the tart is browned, about 25 to 30 minutes.