Line a large baking sheet with parchment paper and set aside. Crumble the cooled chocolate cake up into the bowl with the buttercream. Use your hands or a standing mixer to mix it all together until fully combined.
Form into 1 tablespoon - sized balls and place on the baking sheet. The balls should be no bigger than one tablespoon or they will be too heavy and fall off of the cake pop sticks. Refrigerate for at least two hours or freeze for 1 hour.
Once the cake pops have chilled, prepare your cake pop holder. You can poke holes in a styrofoam box, an upside down cardboard box, or fill a few cups with uncooked rice to put the cake pops into.
When the cake pops have chilled, remove them from the fridge or freezer and melt the chocolate melts or chocolate chips in a microwave-safe mug or glass liquid measuring cup. Microwave for 30 seconds at a time and stir between each interval until the chocolate has melted. If using chocolate chips, add in a little bit of oil at a time to thin out the chocolate if needed. If it's too thick, it will be difficult to dip and the cake balls will fall off of the sticks.
Dip the tip of one end of each cake pop stick into the chocolate then gently push it into one of the cake balls about 3/4 of the way through.
Dip the cake pop into the cup of chocolate and gently turn it and twist until it's fully coated, letting extra chocolate drip off. Dip the cake pops in sprinkles, then place them in the cake pop holder to set. They should set in 30-60 minutes.