When I first made this, I tried building the layers one on top of the other without removing them from the mold. Even with ample time for the peanut butter layer to chill before pouring the grape layer on top of it, the two layers either ended up merging with each other a little or the grape layer ended up dripping down the sides of the peanut butter layer and looking messy. This is why I decided to make each layer separately. You could also save yourself some time and make a double batch of the peanut butter layer and then slice it in half after it cools. I didn't trust myself to slice it perfectly without accidentally ripping it in some spots.