Asparagus Custard Tart

Asparagus Custard Tart

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Ingredients

For crust:
1 cup all-purpose flour
1/2 teaspoon salt
3/4 stick (6 tablespoons) cold unsalted butter, cut into 1/2-inch cubes
1 large egg, lightly beaten
For filling: 1 medium leek (white and pale green parts only), quartered lengthwise, then cut crosswise into 1/3-inch pieces
1 lb medium asparagus, trimmed
1 tablespoon unsalted butter
1/2 teaspoon salt
1/2 teaspoon black pepper
1 1/3 cups heavy cream
3 large eggs, separated
2 teaspoons fresh tarragon, finely chopped
2 teaspoons water

Directions

Blend together flour, salt, and butter in a bowl with your fingertips (or pulse in a food processor) until most of mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Drizzle evenly with egg and gently stir with a fork (or pulse in processor) just until a dough forms.
 
Turn out dough onto a lightly floured surface and divide into 4 portions. With heel of your hand, smear each portion once or twice in a forward motion to help distribute fat. Gather dough into a ball, then flatten into a 5-inch disk. Chill dough, wrapped in plastic wrap, until firm, at least 30 minutes.

While the dough is chilling, wash leek thoroughly in a bowl of cold water, drain (don't dump it out, you really need to lift the leeks out by hand, otherwise you dump all of the grit that settled into the bottom of the bowl back over your formerly clean leeks), then pat dry.  Cook asparagus in a wide 4- to 5-quart pot of boiling salted water, uncovered, until just tender, about 3 minutes (if your asparagus is thicker you might want to cook it longer and peel off the outer layer from the stems). Transfer asparagus to an ice bath to stop cooking, then drain and pat dry. Cut off and reserve tips (leave more stalk if asparagus is thin), then thinly slice stalks crosswise.
Heat butter in a 10- to 12-inch heavy skillet over moderately low heat until foam subsides, then cook leek with 1/4 teaspoon salt, stirring, until softened, 6 to 8 minutes. Stir in sliced asparagus and 1/4 teaspoon pepper and remove from heat.

Put oven rack in middle position and preheat oven to 375°F.

Roll out dough on a lightly floured surface with a floured rolling pin into an 11-inch round, then fit dough inside a tart pan with a removable bottom, pressing dough against bottom edge and side of pan. Place tart pan on a rimmed baking sheet. Run rolling pin over top edge of ring to cut off excess dough.

Whisk together cream, 2 eggs, tarragon, and remaining 1/4 teaspoon salt and 1/4 teaspoon pepper. Lightly beat remaining egg with water in a small bowl and brush tart shell all over with some egg wash. Spoon asparagus mixture into shell, spreading evenly, then pour cream mixture over asparagus.

Bake tart until filling is just beginning to set but still loose on top, 20 to 25 minutes. Scatter asparagus tips over top, pressing lightly if necessary to help them settle into filling, then continue to bake until custard is golden and just set but still slightly wobbly in center, about 30 minutes more (custard will continue to set as it cools).

Cool tart on baking sheet until warm, about 30 minutes. Remove tart from tart pan.  Serve warm or at room temperature, cut into wedges.