Roll the pastry out into a 12-inch circle and then transfer it to a 10-inch tart pan with a removable bottom. Press the pastry into the corners of the pan and trim it to fit the tart pan. Transfer the tart pan to the refrigerator while you prepare the remaining ingredients.

Pre-heat the oven to 375ºF.

Pre-heat a sauté pan over medium-high heat. Add the olive oil and onion and cook for about 5 minutes, until the onion is lightly browned. Crush the whole tomatoes with your hands or a potato masher and add the tomatoes and juice to the onions. Simmer for about 20 minutes, until the sauce has thickened. Remove the sauté pan from the heat and add the butter and parsley. Stir to melt the butter and combine the ingredients and set the pan aside.

Combine the egg and milk in a large bowl. Add the zucchini, half of the Parmesan cheese, Fontina cheese, corn, salt and pepper and toss it all together.

Spread the tomato sauce on the bottom of the pastry in the tart pan. Shingle the coated zucchini slices and corn over the tomato sauce and top with the remaining Parmesan cheese. Cover the tart with aluminum foil and transfer the tart pan to the oven. Bake at 375ºF for 45 minutes. Remove the foil and bake for another 40 to 45 minutes, until the top is nicely browned. Let the tart rest for at least 20 minutes before slicing into wedges and serving.