This recipe is an adaptation/mash-up of the strawberry jam recipe in the book titled Well Preserved by Mary Anne Dragan and the strawberry vanilla jam recipe in the book titled Put 'Em Up! by Sherri Brooks Vinton that also includes my own additions! The butter is optional and will help tame the foaming but don't use more than 1/2 teaspoon as this may raise the pH too high making your finished product unsafe to can. The lemon juice should be bottled instead of fresh because bottled has a more reliable and consistent pH where as fresh can vary. This makes wonderful gifts that are a bit more special than just regular strawberry jam! I usually get 6 half pint jars and a quarter pint jar out of this recipe.