Prepare pie crust into pie or fluted tart pan and refrigerate for at least 30 minutes before filling/baking.: You will notice the dough relax and the butter feeling cool under your fingers as you press it into the pan, which helps the crust bake up flaky and hold its shape. Chilling tightens the gluten just enough so the crust does not slump when you add the filling. A common mistake is skipping the chill, which often leads to a sagging rim and uneven bake, so give it the full rest. If the edges brown too quickly during baking, shield them with foil for the last part of the cook time.
Preheat oven to 425° F.: The oven should smell clean and dry as it reaches temperature, and a quick oven thermometer check ensures accuracy because home ovens can vary. High initial heat helps set the crust quickly and encourages a slight roast on top of the tomatoes , adding depth. Avoid opening the door frequently while the oven lifts to temp, since the fluctuation can affect how the crust sets.
Slice tomatoes into 1/4 inch thick slices removing seeds as you go, and place in a single layer on a paper towel lined surface.: As you slice, note the glossy flesh and the sweet tomato scent; the 1/4 inch thickness keeps slices substantial but not overpowering. Removing seeds reduces excess moisture, and the paper towels will begin to wick away juices, a necessary texture control. If you skip seed removal, you'll likely end up with a runnier filling, which can lengthen bake time to set.
Sprinkle 1 tsp of salt to tomatoes to draw out moisture. Let sit for 30 minutes.: Within minutes you will see beads of tomato juice form on the surface, an encouraging sign that the salt is doing its job. This draw out concentrates flavor and prevents a watery pie, so patience here pays off. A typical misstep is shortening this wait, which often yields a soggy bottom and uneven texture.
Slice shallots very thinly and set aside.: The paper thin shallot slices should look translucent and smell slightly sweet and onion like, which will mellow further in the oven. Thin slicing ensures they integrate into the layers rather than punching through the flavor. If sliced too thick, they remain assertive and can dominate delicate tomato notes.
Combine mayonnaise, egg, all 3 cheeses, salt and pepper. Set aside.: When mixed, the mayo will look glossy and the shredded cheeses will begin to cling, forming a thick, slightly grainy binder that tastes rich and savory. This mixture creates a custard like matrix that holds the slices together as it bakes. Over mixing can break down texture, while under seasoning can leave the pie bland, so taste and adjust gently.
Pat tomatoes dry with a paper towel.: As you press, you'll hear a faint soft sound and see the paper towel darken, proof that excess water is leaving the tomatoes . Drying is essential to keep the filling from loosening, and it helps the top brown rather than steam. Be gentle to avoid mashing the slices, and replace towels if they become saturated too quickly.
Pull out your pie crust and quickly begin layering your ingredients beginning with a third of the cheese mixture at the bottom. Layer a third of your tomatoes in an overlapping pattern, followed by a third of the shallots and basil. Continue to layer in this order so the final layer is overlapping tomatoes, shallot and basil (for a beautiful presentation).: The assembled layers should look intentional and colorful, with ribbons of basil peeking between glossy tomato slices and creamy pockets of cheese mixture beneath. Overlapping creates stability and a pretty top, while alternating flavors ensures each bite is balanced. A common error is overcrowding the crust which prevents even baking, so keep layers thoughtful and avoid pressing them flat.
Bake at 425° for 30-45 minutes.: During baking you will see the top bubble gently and the edges of the crust turn golden brown, while the cheeses melt into a cohesive filling. The aroma will shift from raw tomato to roasted sweetness and toasty cheese notes. If the top is browning too quickly, lower the oven a bit or tent with foil; if the filling still seems loose after the time, allow extra minutes, checking every five to avoid over browning.
Cool completely before cutting into 8 equal slices.: Cooling is when the custard sets fully and the slices hold their shape, so resist the urge to cut hot pie. You should feel the pie firm up and the scent settle into an inviting, concentrated tomato and cheesy aroma. Cutting too early often leads to a sloppy slice and lost layers, so plan ahead and allow proper rest time.
Can be served warm or at room temperature.: The pie offers different pleasures at each temperature, warm for melty comfort and room temperature for a firmer, more pronounced layering of flavors. I often serve a slice slightly cooled so the aromatics are more evident and the texture is ideal. Reheating is fine, but avoid microwave warmth which can make the crust soft; a low oven or toaster oven is preferable.