Place a rack in middle of oven; preheat to 475°F. Arrange tomatoes on a rimmed baking sheet, covering entire surface (it's okay if they overlap). Drizzle with oil; season with salt and pepper. Roast until tomatoes begin to look dry on top, 25-30 minutes. Let cool.
Meanwhile, cook garlic and butter in a small saucepan over medium-low heat, swirling often, until butter foams and milk solids turn golden, 5-7 minutes. Strain garlic butter through a fine-mesh sieve into a heatproof measuring cup; transfer garlic and toasty bits to a cutting board. Finely chop and set aside.
Reduce oven temperature to 375°F. Pulse crackers and 1/4 tsp salt in a food processor until fine crumbs form (you should have about 2 cups). Add eggs and 6 tbsp garlic butter and pulse until mixture is the consistency of wet sand; set remaining garlic butter aside. Transfer to a springform pan. Using a flat-bottomed measuring cup, press crumbs firmly onto bottom and 1 1/2" up sides of pan. Bake crust until edge is just starting to take on colour, 8-10 minutes. Transfer pan to a wire rack and let crust cool.
Mix Taleggio, Parmesan, mayonnaise, chopped thyme, remaining 1/2 tsp salt, remaining 1/4 tsp pepper, and reserved chopped garlic and bits in a medium bowl. Gently dollop half of cheese mixture over bottom of crust, then spread into an even layer with an offset spatula (don't press too hard or you will break the crust). Layer half of tomato slices over and press down to even out layers. Repeat with remaining cheese mixture and tomatoes. Brush remaining garlic butter over tomatoes. Top with shallot and thyme leaves.
Set pan on a rimmed baking sheet and bake pie until filling is bubbling vigorously and crust is browned, 60-70 minutes. Transfer to rack and let cool 1 hour before serving.Do ahead: Pie can be made 1 day ahead. Cover loosely and chill.Special Equipment: A 9" diameter springform pan.
-You can substitute the Taleggio cheese for Fontina cheese.
-I found it took more than 6 tbsp of garlic butter to moisten the crumbs enough to stick together, however, there was still plenty of garlic butter left to brush on the top. So use what you need to get the crumbs right.