To make the pie crust add the crackers to a food processor fitted with a steel blade and process until they have broken down into fine crumbs.
Add the melted butter and parmesan cheese and process until everything is combined. Pour this mixture into a nine-inch pie plate. Use your hands or the smooth bottom of a glass to press the mixture down evenly and up the sides of the pie plate.
Bake for 10-12 minutes or until the crust is golden brown. Remove from the oven and let cool.
While the crust is baking, slice the tomatoes (no need to blanch them or peel them). Sprinkle with a little salt and let the slices drain on a paper towel for at least 20 minutes. Blot the tops of the tomatoes with a paper towel to remove any additional moisture.
When the crust is cool, sprinkle 1/3 of the grated cheese over the bottom. Add a layer of sliced tomatoes and season with salt and pepper. Repeat with another layer of cheese and tomatoes and top with the rest of the grated cheese. Top with any remaining salt and pepper. (You should have three layers of cheese and two layers of tomatoes.)
Mix the mayonnaise, parmesan cheese, and Dijon mustard in a small bowl and spread evenly over the top of the cheese using a knife or offset spatula.
Bake for 20 minutes or until the topping is lightly browned and the mixture is bubbly.
Remove from the oven and place on a wire rack to cool. Let the pie cool for at least 35 minutes before slicing it.
Serve warm or at room temperature.
This dish is best served fresh the day you make it. I prefer it at room temperature, but it can also be eaten cold or warm. Leftovers can be stored covered in the refrigerator for up to two days. I do not recommend freezing them. If you don't have Ritz crackers, try substituting saltine crackers or cheese crackers instead. Don't skip the step of letting your tomato slices drain and make sure to remove as much moisture as possible by blotting them with paper towels. If not, your pie will be soggy. If you don't have a food processor, place the crackers in a plastic bag and use a rolling pin or the heel of your hand to crush them into fine crumbs. If you are using a regular pie crust, be sure to follow the directions to prebake it first and let it cool completely before adding the filling. For the best results, let the finished pie cool for at least 35 minutes to give it time to set up a bit before you cut into it.