Preparation / Directions:
Shuck corn, reserving largest outer husks (about 20 to 24) for wrapping salmon and tearing some remaining husks lengthwise into narrow strips for tying packages.
Grill corn on a rack set 5 to 6 inches over glowing coals, turning it frequently, until browned (not blackened) all over, about 12 minutes, and cool to room temperature. Cut kernels from cobs (there will be about 1 3/4 cups) and in a bowl stir together with chipotle powder and butter until combined well.
On a work surface arrange 5 to 6 large husks side by side, overlapping long sides. Arrange a salmon piece in the center with length parallel to long sides of husks and top with one fourth corn mixture, one fourth epazote, and one fourth scallion. Fold long sides and ends of husks over filling and tie with strips of husks. Make 3 more packages in same manner with remaining husks, corn mixture, epazote, and scallion.
Grill packages around edges (to avoid hottest part of coals) of a rack set 5 to 6 inches over glowing coals, covered, turning them once, until husks are charred and salmon is just cooked through, about 6 minutes on each side. (Packages may open while cooking, and butter might drip, causing flare-ups.)