How to Make It
Use paper towels to pat chicken breast halves dry. Brush on all sides with olive oil. Mix ancho chili powder, dark brown sugar, paprika, cayenne and a generous pinch each of salt and pepper in a bowl. Rub chicken with spice mixture. Wrap chicken in plastic wrap and refrigerate for at least 15 minutes or up to several hours.
Light a charcoal grill and let burn to a gray ash (or preheat a gas grill to medium-high). Alternatively, preheat broiler to high. Set grill rack or broiling pan about 6 inches from heat source. Season chicken with salt and pepper. Place chicken on lightly oiled grates or broiling pan and cook until browned, about 4 minutes. Turn and continue cooking until firm to the touch and cooked through, about 5 minutes longer. Remove to a work surface, cover loosely with foil and let rest for 5 minutes. Cut into thick slices on the bias and serve.