Nothing says summer in the South of France like long, lazy outdoor meals prepared with lots of garden fresh produce, all accompanied by bottle of crisp, cold, dry Rosé wine. This classic French jam combines both! Make it when raspberries are in season, and open a jar of summer in the winter.
In a large saucepan, combine all ingredients. Using a potato masher, crush the raspberries until completely broken down.
Bring mixture to a boil over high heat, stirring often with a wooden spoon. Once mixture reaches a full boil, add butter and reduce the heat to medium. Continue to cook and stir until jam has thickened, about 12 minutes. If you want a firmer set, return mixture to a hard boil and add pectin all at once. Continue to boil, stirring constantly, for one minute.
Fill hot, prepared jars. Run a spatula or knife around the inside of each jar to eliminate air bubbles. Thoroughly wipe the rim of each jar clean with a damp paper towel. Place lids. Tighten rings to fingertip tightness.
Process in a boiling water bath for 10 minutes. Remove to a clean dish towel away from direct sunlight. Allow to rest for 12 hours. Check for seal. Refrigerate or reprocess any unsealed jars. Sealed jars will keep for up to one year in a cool, dark cupboard. Once opened, jam will keep for up to three weeks in the fridge.