Asparagus Tart

1 tablespoon all-purpose flour, plus more for dusting

1 sheet frozen puff pastry, thawed (a 9 1/2- by 9-inch sheet from a 17.3-ounce package)

1 cup mascarpone

1 1/2 teaspoons kosher salt

1 large egg, beaten

1 lemon, zest finely grated (about 1 tablespoon)

1 tablespoon chopped fresh chives

1 tablespoon chopped fresh tarragon

1 pound pencil asparagus, woody bottoms trimmed off

1 tablespoon olive oil

Freshly ground black pepper

Lightly dressed greens, for serving