Crumble cake into smaller pieces. Add in frosting.
Mix in the frosting until fully incorporated. Test the mixture by taking a small portion and rolling it into a ball. If it holds its shape then it is ready. If not, add more frosting until the cake comes together.
Place the candy melts or chocolate in a heat proof bowl (minus about 2 tablespoons). Make sure that there is no water or any moisture in the bowl or the utensils you are using.
To melt the chocolate, melt the chocolate on 50% power for 30 seconds. Stir the chocolate. Return to the microwave and melt the chocolate again at 50% for 30 seconds (or 15 seconds for white chocolate). Stir again. If the chocolate has mostly melted, add the reserved chocolate, to the bowl and stir until all the chocolate has fully melted. If the chocolate has not fully melted, return to the microwave for 15 seconds increments at 50% power until melted.
Using a spoon or a food-safe brush, pour some of the melted chocolate in each of the molds. Spread the chocolate using a spoon or food safe paintbrush, so the mold is fully covered in chocolate.
Wipe off any excess chocolate on the corners.
Place in the fridge for 10-15 minutes until fully firmed.
Remove from the fridge. If you notice any holes in the chocolate at this point, coat with additional chocolate and return to the fridge for another 10-15 minutes.
Once coated and firm, add about 1 tablespoon of the cake mixture and press it into the mold. Make sure not to overfill it so you have a little space to seal it with more chocolate. Place into the fridge for about 10 minutes now.
Spoon more melted chocolate or candy melts on the top of the mold. Use a spatula or back of a spoon to spread it on to seal the back.
Wipe off any excess around the edges and place mold in the fridge for about 30 minutes until everything is firm.
Once firmed in the fridge, carefully peel the chocolate gem from the mold. At this point you can clean up the edges with a peeler to remove any frayed edges.
Decorate the Heart CakeGems with a drizzle of white chocolate and your favourite sprinkles. You can also use gold or silver leaf, as well as some gold spray or lustre dust for extra sparkle!
These cake gems will keep at room temperature for 2-3 days.