Instructions

1. In a medium saucepan over medium-high heat, add the blueberries, lemon juice, and granulated sugar. Give it a gentle stir. When the mixture starts to bubble around the edges, turn the heat to low, stirring often. The mixture will start to bubble more and foam up. When it starts to foam, add in the 1/2 teaspoon of butter and stir in.
2. Cook for about 15-20 minutes or until the mixture is thickened. You should end up with about 1 cup of blueberry filling.
3. Transfer the mixture to a bowl and allow it to cool completely. *To speed up the process, add the bowl to the fridge for about 30 minutes or so.