Clean your Pop It toy super well with soap and warm water. Dry completely.
Layer M&M's over the bubbles (if you're OCD like we are, make sure the "M" is laying down so when you release the chocolate the M will be facing up).
Pour melted chocolate over the candies in an even smooth layer. Make sure there are no gaps and shakedown gently on the counter to even out air bubbles.
Freeze uncovered until hardened - it took us just 30 minutes in our freezer. Pop out the chocolate gently and break them into bars.
