Prepare and prebake one 11-inch short-crust pastry shell according to recipe directions.
Set aside.
While the crust bakes, prepare the leeks. Trim the dark green tops and roots from the leeks.
Slice them in half lengthwise and rinse thoroughly under cold water to remove any grit. Thinly slice the white and light green parts.
In a medium skillet over medium heat, melt the butter.
Add the sliced leeks and sauté for 8-10 minutes, until softened and just beginning to turn golden.
Season with salt and pepper.
In a small bowl, toss the grated Swiss and Romano cheeses with the flour until evenly coated.
In a separate large bowl, whisk together the eggs, cream, and a pinch of salt until smooth.
Assemble the quiche.
Spread the sautéed leeks in an even layer over the bottom of the prebaked pastry shell.
Sprinkle the cheese mixture evenly over the leeks. Carefully pour the egg and cream custard over the top.
Arrange the thinly sliced tomatoes in a single layer over the custard. Lightly season the tomatoes with a sprinkle of salt and a grind of fresh black pepper.
Bake in a preheated oven at 400°F / 200°C for 15 minutes.
Then, reduce the oven temperature to 325°F / 165°C and continue to bake for another 30-35 minutes, or until the center is just set and a knife inserted near the middle comes out clean.
Let the quiche cool on a wire rack for at least 15 minutes before slicing.
Serve warm or at room temperature.
