In a large, nonstick pan, melt 3 tablespoons of the butter, add the mini marshmallows and cook over medium heat, stirring constantly, until the marshmallows are melted. Add the rice krispies and stir until combined. Pour into a 9x9” pan which has been sprayed with nonstick cooking spray. Pack the mixture firmly together by pressing it with the palm of your hand. Allow to cool before cutting into 9 even squares with a sharp knife.
Repeat the above process for the Cocoa Krispies and Fruit Pebbles.
In two shallow, microwave-safe containers, melt the white and milk chocolate chips. To make sure you aren’t over-cooking the chocolate, microwave each container of chips for no more than 30 seconds at a time, stir, then return to your microwave for an additional 30-seconds. Continue doing this just until the chocolate is smooth.
Dip the tops of the Rainbow Krispie squares into the white chocolate. Sprinkle with rainbow jimmes, then transfer to a cooling rack until the chocolate is hardened. Do the same for the Cocoa Krispies, only dip these squares in melted milk chocolate, then top with mini M&M’s. Finally, dip the original Rice Krispies into white and dark chocolate, then press them into rainbow sprinkles. If you plan to place candles on top of your cake, use a skewer to press holes into one of the Rainbow Krispies just after you’ve dipped it into the chocolate & added sprinkles. Press the candles gently into these holes, then allow the chocolate to harden around the candles.
Once all chocolate has firmly hardened, arrange the Rice Krispies on a cake pedestal. We placed 8 of the Rainbow Krispy Squares on the bottom of the pedestal, filling in the center of this circle with Cocoa Krispy Squares, then topping with 5 Cocoa Krispy Squares, 4 Rice Krispy Squares, then topped it off with a single Rainbow Krispy and extra-long candles purchased from Hobby Lobby.