In a medium saucepan over medium-high heat, add the strawberries 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.
Cook for about 10-15 minutes or until the mixture is thickened and, when you run a spatula through it the line mixture stays separated and just barely starts to melt back together. Transfer to a jar or bowl that you can cover once cooled.