Seared Prosciutto-Wrapped Asparagus

from Saveur magazine (edited so as not to use the word judiciously, because i don't know the word)

1/2 C balsamic vinegar
36 thick spears asparagus, trimmed
18 slices prosciutto
3 Tbsp butter
salt

Put vinegar into saucepan and simmer over medium heat until reduced by about two-thirds and slightly syrupy, 8-10 minutes. Remove from heat and set aside. Meanwhile, steam asparagus in a steamer basket set over a pot of boiling water over high heat until just tender, about 4 minutes. Set asparagus aside. Lay 1 slice of prosciutto on a clean surface with one narrow end closest to you. Put 2 asparagus spears on end closest to you, perpendicular to prosciutto, with tips facing same direction. Roll up prosciutto around asparagus and set aside. Repeat with remaining prosciutto and asparagus. Working in 3 batches, melt 1 Tbsp butter in large, heavy bottomed skillet over medium-high heat. Add 6 bundles, season with salt, and cook until browned on each side, about 45 seconds per side. Transfer to warm plate. Repeat process with remaining butter and bundles. Serve bundles drizzled with vinegar syrup