Place white chocolate buttons in a heatproof bowl, and melt in microwave following the packet instructions. (If there is no instruction, place chocolate in microwave and melt on high for 60 seconds. Stir, and return the chocolate to the microwave, and heat for another 30 seconds. Stir again)

Pour melted chocolate into a baking tray lined with parchment paper. Spread it lightly to form a rectangle. Decorate with M&Ms. Press the chocolate buttons lightly into the white chocolate. Set aside for 2 hours in room temperature, or refrigerate for 20 minutes until firm.

Use a sharp knife or your hands to break it up into uneven pieces. Serve at room temperature.