This recipe came from an internet blog called ShowFood Chef and was created by chef Cathy Shambley. I have changed it ever so slightly (almost not at all!) and it is really fantastic! The butter will help reduce foaming - don't add more than 1/2 teaspoon because that could raise the pH too much for safe canning. The lemon juice should be bottled because fresh lemon juice varies in acidity while bottled provides consistent acidity.