Feel free to use small (4-in.-wide) tortillas, if you can find them; then this recipe makes enough filling for 8 tacos. Time: 20 minutes.
3 fresh poblano chiles (about 10 oz. total)
1 white onion (about 1/2 lb.), thinly sliced
1 tablespoon butter
1/4 pound jack cheese, cut into thick slices
4 to 6 warm corn or flour tortillas (6 to 7 in. wide)
How to Make It
Preheat broiler. Put chiles on a baking sheet and broil about 3 in. from heat, turning as needed to char and blister on all sides, about 8 minutes total. Let cool. Discard stems and seeds. Cut chiles into thin strips.
Meanwhile, in a 6- to 8-in. frying pan over medium-high heat, cook onion in butter, stirring often, until softened, 4 to 5 minutes.
Stir in chile strips and top with a layer of cheese slices. Cover and cook over low heat until cheese melts, about 2 minutes. Scoop hot chile mixture into tortillas.