Hi I recently made a layer bar with a crust and then about a half inch of caramel on top. I melted caramel candies from the store because I do not have enough experience yet to make my own. I wanted the bars to set and not spread out after cutting so they could be held and eaten on the go if necessary. So I put them in the fridge. The caramel hardened to a point where it was inedible! I added some vanilla when melting because that is what the recipe called for. What should I do to make them stay gooey yet stable next time?