1. Make your favorite cake batter and separate it into 6 small bowls.
2. Color each bowl a color of the rainbow (use gel coloring for best results).
3. Pour each color into a piping bag and cut a small hole in each tin.
4. On a prepared jelly roll pan, pipe the batter in lines in the order of the rainbow.
5. Bake at 325 for 10-12 minutes.
6. Once cooled, cut out shamrocks using a cookie cutter (be sure to make pairs; 2 shapes per cake).
7. Add homemade marshmallow fluff to the bottom shamrock, then top with another to make a sandwich.
8. Freeze for up to an hour to set.
9. Dip into white candy melts and top with rainbow sprinkles right away.
10. Add green lines to complete the cakes

For the marshmallow fluff

1. Place water, sugar, and corn syrup in a medium saucepan. Stir to combine.
2. Insert a candy thermometer into the pot and heat over medium-high. Do not stir from this point on.
3. Wipe down your mixer bowl with lemon juice or vinegar to make sure it’s grease free.
4. Add egg whites and cream of tartar in the bowl of a stand mixer.
5. When the sugar syrup reaches 225°F, start whipping the egg whites to soft peaks (about 4 minutes).
6. When the sugar syrup reaches 240°F remove from the heat, turn mixer to medium and very slowly and carefully pour the sugar syrup into the whites in a thin, steady stream.
7. Once all of the syrup is in, set mixer to medium/high and whip.
8. Continue to whip until the mixture is thick and fluffy (about 8 minutes).
9. Add in vanilla and whip until the fluff has cooled completely.
10. Use right away or store for up to 2 weeks at room temperature.