Instructions:
- Prepare the Pie Dough: Pulse flour and salt in a food processor. Cut in the cold butter until coarse crumbs form. Gradually add ice water until the dough just comes together. Form into a disc, wrap, and chill for 1 hour.
- Pre-bake the Crust (Blind Bake): Roll out the chilled dough and carefully fit it into the 9-inch pie dish. Trim and crimp the edges. Line the crust with parchment paper, fill with baking weights, and blind bake at 400°F (200°C) for 15 minutes. Remove weights/paper and bake for another 5–7 minutes until lightly golden. Cool completely.
- Prep the Tomatoes: Slice tomatoes evenly. Lay them on paper towels, sprinkle lightly with kosher salt, and let them sit for 30 minutes to draw out excess water. Pat them thoroughly dry before using.
- Prepare the Custard Base: In a medium bowl, whisk together the egg, mayonnaise, 2 tablespoons flour, Dijon mustard, pepper, and cayenne until completely smooth.
- Assemble the Pie: Sprinkle the bottom of the cooled crust with the grated Cheddar and Parmesan cheeses. Layer the dried tomato slices tightly in a single layer, slightly overlapping. Sprinkle with fresh basil.
- Pour and Bake: Slowly and evenly pour the mayonnaise-custard mixture over the tomatoes, ensuring it seeps into all the gaps. Bake at 375°F (190°C) for 50–60 minutes, or until the filling is set (minimal jiggle in the centre) and the top is golden brown.
- Cool Completely: Allow the pie to cool on a wire rack for at least 1 hour before slicing. This allows the filling to firm up properly. Serve warm or at room temperature.