Place blackberries in a 2-quart casserole; microwave at MEDIUM (50% power) for 4 to 5 minutes, stirring after half the defrosting time.
Stir again; let stand 5 minutes.
Add sugar; let stand 20 minutes, stirring occasionally.
Combine pectin and water in a 4-cup glass measure; stir well.
Microwave at HIGH for 2 to 2 1/2 minutes or until boiling.
Boil for 1 minute, stirring after 45 seconds.
Stir well again, and pour over the fruit.
Stir for 3 minutes.
Pour into sterilized jelly glasses or frozen food containers.
Cover with lids, and let stand at room temperature 1 to 2 hours or until jelled.
Store in freezer up to 1 year or refrigerator up to 3 weeks.
To serve, remove and allow coming to room temperature.