Sorrel imparts a lovely lemony tang to spinach. Although a half pound each of the greens may look like too much, they cook down dramatically.
For the Black-Pepper Pate Brisee
- 2 1/2 cups all-purpose flour
- 1 teaspoon sugar
- 1 teaspoon coarse salt
- 1 1/2 teaspoons coarsely ground pepper
- 1 stick cold unsalted butter, cut into small pieces
- 1/4 to 1/2 cup ice water
For the Filling
- 1/4 cup extra-virgin olive oil
- 3 1/2 cups thinly sliced onions (1 pound)
- 1 1/2 tablespoons minced garlic (4 cloves)
- Pinch of red-pepper flakes
- 1/2 pound spinach, stems removed
- 1/2 pound sorrel
- All-purpose flour, for rolling
- Coarse salt
- 6 to 8 ounces Morbier cheese, rind removed and sliced lengthwise into long pieces
Make the black-pepper pate brisee: Preheat oven to 400 degrees, with rack in lowest position. Pulse flour, sugar, salt, and pepper in a food processor until combined. Add butter, and process until mixture resembles coarse meal, about 10 seconds. Drizzle 1/4 cup ice water over mixture. Pulse until mixture holds together when pressed between 2 fingers. If dough is too dry, add more water, 1 tablespoon at a time, and pulse. Shape dough into 2 disks, and wrap each in plastic wrap. Refrigerate dough until firm, at least 1 hour and up to 2 days.
Make the filling: Heat oil in a large saute pan over medium heat. Cook onions, garlic, and red-pepper flakes until onions are softened and just starting to turn golden, about 10 minutes. Add spinach and sorrel, and cook, stirring with tongs, until greens just wilt, about 2 minutes. Let cool.
To assemble: Roll out each piece of dough to an 11-by-14-inch rectangle on lightly floured parchment, and transfer to 2 baking sheets. Divide filling between rectangles, leaving a 2-inch border all around. Season filling with salt, and fold in edges of dough. Refrigerate 1 tart, and bake the other until edges are golden, about 35 minutes. Place half the cheese on top of filling, and bake until cheese is melted, 5 minutes more. Bake remaining tart in same manner. Serve tarts warm or at room temperature.