Prepare the Tomatoes:

Slice the Tomatoes: Slice the tomatoes about 1/4-inch thick. Lay them on paper towels or a clean kitchen towel. Sprinkle the slices lightly with kosher salt and let them sit for about 10-15 minutes. This process helps draw out excess moisture, preventing the pie from becoming soggy. Afterward, gently pat the tomato slices dry with another paper towel.

Preheat the Oven:

Preheat your oven to 350°F (175°C).

Assemble the Pie:

Layer the Tomatoes: Spread a thin layer of Dijon mustard over the bottom of each pre-baked pie crust. Arrange the tomato slices in a single layer in the crusts, overlapping them slightly. Add a pinch of black pepper and minced onion over the tomatoes.

Add the Onion and Pimentos: Evenly distribute the grated Vidalia onion and drained pimentos over the tomato layer.

Prepare the Cheese Mixture:

In a large bowl, combine the mayonnaise, sharp cheddar cheese, Monterey Jack cheese, and Parmesan cheese. Mix until the ingredients are well combined. Add a pinch of kosher salt, black pepper, and sugar (if using) to taste. The mixture should be thick and spreadable.

Top the Pie:

Spread the Cheese Mixture: Spoon the cheese mixture over the tomato and onion layers in each pie, spreading it evenly to cover the entire surface. This creates a creamy, cheesy topping that will turn golden and bubbly as it bakes.

Bake the Pie:

Place the pies in the preheated oven and bake for 25-30 minutes, or until the top is golden brown and the cheese is melted and bubbly. If needed, shield the crust edges with aluminum foil to avoid excessive browning.

Garnish and Serve:

Remove the pies from the oven and let them cool for at least 10 minutes to set.