SPICY RED-PEPPER JELLY

Steps:

• Sterilize jars and lids:
• Wash jars, lids, and screw bands in hot, soapy water, then rinse well. Dry screw bands. Put empty jars on a rack in a boiling-water canner or a deep 8- to 10-quart pot and add enough hot water to cover by 2 inches. Bring to a boil, covered, then boil 10 minutes. Remove canner from heat, leaving jars in water, covered. Heat lids in water to cover by 2 inches in a small saucepan until thermometer registers 180°F (do not let boil). Remove from heat. Keep jars and lids submerged in hot water, covered, until ready to use.
• Make jelly:
• Pulse bell peppers with red-pepper flakes in a food processor until finely chopped. (Mixture will measure about 2 1/2 cups.)
• Whisk together pectin and 1/4 cup sugar in a small bowl.
• Stir 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.
• Carefully 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.
• Seal and process jars:
• Put 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.
• After 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).