all-purpose flour, plus more for dusting • frozen puff pastry, thaw 9.5 by 9" sheet frm 17.3-oz pkg • mascarpone • kosher salt • large egg, beaten • lemon, zest finely grated (about 1 tablespoon) • chopped fresh chives • chopped fresh tarragon • olive oil • pencil asparagus, woody bottoms trimmed off • Freshly ground pepper • Lightly dressed greens for serving