Put half the berries (2 pints) Blueberries in cooking pot and crush the berries to make juice.
Stir in remaining 2 pints berries and lemon juice and zest.
Add sugar and butter and bring to a full, rolling boil that cannot be stirred down. Pay careful attention to the pot, it will boil over in a heartbeat.
When berries reach the full, rolling boil, add the pectin. Stir for 1 minute
Remove from heat and ladle into jars.
Follow canning instruction. You will have 7 half pints.