1 1/2  pound         ground beef sirloin
                        salt and freshly ground pepper
     1/2  teaspoon      cumin
     1/2  teaspoon      paprika
     1/4  teaspoon      chili powder
   4                    fresh anaheim chiles
   1                    fresh poblano chile
   3      tablespoons   vegetable oil
     1/4  cup           minced onion
   1                    garlic clove -- minced
   1 1/2  teaspoon      all-purpose flour
     1/3  cup           water
   4      thick slices  cheddar cheese
   4                    hamburger buns
In a large bowl gently but thoroughly combine the ground beef, salt,
pepper, cumin, paprika, and chili powder. Gently form the meat into
four 6 ounce patties, about 1/2-inch thick, and place on a plate.
Refrigerate the burgers, covered until needed.
Preheat broiler or grill. Char the chiles on all sides, turning
occasionally with tongs, about 5 to 10 minutes. Transfer blackened
chiles to a large bowl and cover tightly with plastic wrap. Let stand
for 30 minutes or until cool enough to handle. Wearing rubber gloves,
peel the chiles. Trim off stems, slice in half and discard seeds and
ribs. Coarsely chop the chiles.
In a saucepan heat the oil over moderate heat and cook the onion until
soft. Add the garlic and cook for another minute. Add the flour and
cook for 2 minutes, stirring to coat. Slowly add the water, stirring
to combine, and bring the mixture to a simmer. Stir in the chiles and
cook until thickened. Season to taste with salt. Keep warm.
Cook the burgers to desired degree of doneness. Top each burger with a
slice of cheese and cover, cooking until cheese melts. Transfer each
burger to a bun and top with chile mixture. Serve immediately.