Step 1: Prepare your canning jars and lids by washing them thoroughly. Sterilize jars by boiling them for 10 minutes; keep hot until ready to fill. Place lids in hot (not boiling) water.
Step 2: Wash bell peppers and jalapeños. Remove stems, seeds, and membranes from bell peppers. For jalapeños, remove stems, and adjust seed/membrane removal based on desired heat level (wear gloves!). Roughly chop all peppers.
Step 3: Place chopped peppers in a food processor and pulse until very finely minced, but not puréed. You want small, consistent pieces for the best texture in this pepper jelly recipe.
Step 4: In a large, heavy-bottomed pot, combine the minced peppers, white vinegar, and about 1/4 cup of the granulated sugar with the powdered pectin. Stir well to dissolve the pectin.
Step 5: Place the pot over high heat and bring the mixture to a full, rolling boil that cannot be stirred down. Continue boiling for exactly 1 minute, stirring constantly to activate the pectin.
Step 6: Immediately add the remaining granulated sugar all at once. Stir continuously until the sugar is completely dissolved.
Step 7: Bring the mixture back to a full, rolling boil. Boil hard for exactly 1 minute, stirring constantly. Watch carefully as it will foam up.
Step 8: Remove the pot from the heat. Skim off any foam from the surface of the jelly using a metal spoon. A tiny pat of butter added at the beginning can sometimes help reduce foaming.
Step 9: Carefully ladle the hot pepper jelly into your hot, sterilized canning jars, leaving 1/4 inch of headspace. Wipe the rims clean with a damp cloth.
Step 10: Place the hot lids on the jars and screw on the bands finger-tight. Do not overtighten.
Step 11: Place the filled jars into a boiling water canner, ensuring they are fully submerged by at least 1-2 inches of water. Bring the water back to a rolling boil and process for 10 minutes (adjust for altitude if necessary).
Step 12: Carefully remove the jars from the canner and place them on a towel-lined counter, spaced apart. Let them cool undisturbed for 12-24 hours. Check seals; store properly sealed jars in a cool, dark place for up to a year. Refrigerate unsealed jars and consume within 3 weeks.