Blueberry Jam

4 c. blueberries
3 1/2 c. sugar
Zest and juice of 1 lemon

In medium saucepan over medium heat combine berries, sugar, zest and juice, stirring well and mashing about 1/4 of the berries. Continue to cook about 45 minutes until thickened. Pour into clean canning jars and seal. Process in boiling water 20 minutes.