- a 1/2-pound frozen puff pastry sheet, thawed
- 1 bunch scallions (white and pale green parts only), sliced thin (about 3/4 cup)
- 1 tablespoon unsalted butter
- 1 pound asparagus, trimmed and cut diagonally into 1/4-inch-thick slices, reserving tips
- 3 large eggs
- a 3 1/2-ounce log soft mild goat cheese such as Montrachet
- 1 cup milk
- 3/4 teaspoon salt
- 1 tablespoon finely chopped fresh tarragon leaves or 3/4 teaspoon dried, crumbled
- On a lightly floured surface, roll out pastry into a 16-inch square and fit into an 11-inch tart pan with a removable fluted rim. Roll a rolling pin over top of tart to trim pastry flush with top of rim. Chill pastry shell while making filling.
- Preheat oven to 425°F. with a baking sheet on lowest rack.
- In a small skillet, cook scallions in butter with salt to taste over moderate heat, stirring, until softened, about 1 minute, and cool.
- In a steamer set over boiling water, arrange asparagus slices and top with reserved tips. Steam asparagus, covered, until crisp-tender, about 2 to 3 minutes, and drain well, reserving tips separately.
- In a blender, blend eggs, goat cheese, milk, and salt with pepper to taste. Add tarragon and pulse custard to combine.
- Spread scallions and asparagus slices in pastry shell and arrange reserved tips decoratively on top. Pour custard slowly over vegetables.
- Bake tart in pan on heated baking sheet in oven 15 minutes. Reduce temperature to 375°F. and bake tart until set, about 8 minutes. Transfer tart in pan to a rack.
- Remove rim of pan and serve tart warm or at room temperature.