In a food processor, pulse together all-purpose flour and salt. Add cold butter and pulse until it resembles small peas. Combine egg yolk with cold water, drizzle into the processor while mixing until crumbly. Form into a disk and chill for 30 minutes.

Preheat your oven to 400°F (200°C). Slice tomatoes into rounds, place on a wire rack, and let drain for 10-15 minutes. Pat dry to avoid sogginess.

In the food processor, combine parsley, basil, thyme, and garlic. Add salt and pepper. Drizzle in olive oil until a paste forms and toss with the drained tomatoes.

Roll chilled dough into a 10x15-inch rectangle, transfer to a baking sheet, and press into corners. Line with foil, fill with weights, and bake for 15 minutes. Cool and lower oven to 375°F (190°C).

Brush the crust with Dijon mustard, sprinkle cheese over the base, arrange tomatoes and herb mixture, then add another layer of Gruyere.

Bake for 30 minutes until cheese is golden and bubbly. Let cool slightly before slicing.