Prepare JARS: Boil jars on rack in large stockpot filled with hot water 10 min. Meanwhile, place flat lids in saucepan; cover with water. Bring to boil; remove from heat. Let jars and lids stand in hot water until ready to use. Drain well before filling.
Prepare PECTIN MIXTURE: Gradually add pectin to boiling water in medium bowl, stirring constantly. Let stand 10 min. or until pectin is completely dissolved, stirring occasionally.
Trial BATCH: Measure 1 cup unset jam or jelly, 2 Tbsp. sugar and 1 Tbsp. Pectin Mixture (from step 2) into small saucepan. Bring to full rolling boil (a boil that doesn't stop bubbling when stirred) on high heat, stirring constantly. Boil 30 sec., stirring constantly. Remove from heat. Skim off any foam. Pour jam or jelly into prepared jar; cover. Let stand 24 hours before checking set. Refrigerate remaining Pectin Mixture.
Remainder OF BATCH: Do not remake more than 8 cups of jam or jelly at one time. If Trial Batch sets, follow the recipe above, using listed measures of sugar and Pectin Mixture for each 1 cup of jam or jelly. Measure jam or jelly into stockpot. Bring to full rolling boil; boil 30 sec., stirring constantly. Remove from heat. Skim off any foam with metal spoon. Ladle into sterilized jars, filling to within 1/4 inch of tops. Wipe jar rims and threads. Cover with two-piece lids. Screw bands tightly. Discard any leftover pectin mixture.
PROCESS JARS: Bring boiling-water canner, half full with water, to simmer. Place jars on elevated rack in canner. Lower rack into canner. (Water must cover jars by 1 to 2 inches. Add boiling water, if necessary.) Cover; bring water to gentle boil. Process 5 min. for jelly, or 10 min. for jam. Remove jars and place upright on towel to cool completely. After jars cool, check seals by pressing middle of lids with finger. (If lid springs back, lid is not sealed and refrigeration is necessary.)