Chocolate Filling won’t thicken
This is my recipe. I cup sugar, I cup hot water, 2 heaping tablespoons powdered baking chocolate, 2 heaping tablespoons cornstarch. Mix together, add hot water over medium/high heat, keep stirring until thickened, add tsp butter at the end. Put in the fridge to cool and thicken. This goes in between 2 chocolate cake layers. It always ends up running out of the cake. HELP!!