Pulse 4 coarsely chopped red bell peppers and 2 coarsely chopped red chiles (such as Fresno) in a food processor until very finely chopped (be careful not to purée). Transfer to a large saucepan and add 3 cups sugar and 1 1/2 cups apple cider vinegar. Bring to a boil, reduce heat, and simmer until liquid is reduced by twothirds, about 1 hour.
Transfer jelly to heatproof jars; cover and chill until set, about 4 hours.
