Preheat the oven to 350°F.
Brown the sausage in a heavy-bottomed pan, breaking up any large clumps with a spatula. Drain and reserve.
While the sausage is cooling, combine the fontina, shallot, roasted peppers, basil, mayonnaise, and Dijon mustard in a large mixing bowl.
To assemble, place the desired amount of cheese mixture in the bottom of the pie shell and layer tomatoes on top alternating sizes and colors of tomatoes.
Bake for 35 to 45 minutes or until the cheese is bubbly and the edges of the crust are golden.
Allow the pie to cool completely to room temperature before serving.