A dash of red pepper flakes adds nuance to this condiment of sweet red peppers cooked with vinegar, sugar, and pectin. Serve it on a cheese board or stir a spoonful into mayo for a vibrant sandwich spread.
03Whisk together pectin and 1/4 cup sugar in a small bowl.
04Stir together pepper mixture, vinegar, butter, salt, and remaining 3 cups sugar in a 5- to 6-quart heavy pot. Bring to a vigorous boil over high heat, then continue to boil vigorously, stirring occasionally, 5 minutes. Gradually add pectin mixture, whisking constantly. Return jelly to a vigorous boil, stirring constantly, and boil, stirring constantly, 1 to 2 minutes (mixture will thicken slightly). Remove from heat.
05Carefully remove jars and lids with canning tongs, then drain jars upside down on a clean kitchen towel and quickly dry lids. Invert jars and immediately ladle hot jelly into jars, leaving 1/4 inch of space at top. (Last jar may not be full.) Run a clean plastic spatula between jelly and sides of jars to eliminate air bubbles. Wipe off rims of filled jars with a damp clean kitchen towel, then firmly screw on lids with screw bands.
06Put sealed jars on rack in canner or pot and add enough hot water to cover by 2 inches. (If you have a jar that is partially full, do not process it. Cover it with a lid and screw band, then keep in refrigerator.) Bring to a full boil, covered, then boil jelly, covered, 15 minutes. Transfer jars with canning tongs to a towel-lined surface to cool. Jars will seal; if you hear a ping, that means that the vacuum formed above the cooling jelly has made the lid concave. Remember that you may or may not be around to hear the ping. The important thing is for the jars to eventually have concave lids. Jelly will thicken as it cools.
07After jars have cooled, 12 to 24 hours, press center of each lid to check that it's concave, then remove screw band and try to lift lid with your fingertips. If you can't, the lid has a good seal. Replace screw band. Put any jars that haven't sealed properly in the refrigerator and use them first (along with jar that was only partially full).