Preheat the oven to 350 and line a large baking sheet with a silicon mat or parchment paper.

Mix the cake mix, milk, oil, and eggs until smooth and thoroughly combined. Add in jimmies and just fold in. Do not over stir and cause the colors to run.

Measure out dough with a cookie scoop or use a tablespoon to measure.

Bake for 10 minutes. Remove from the oven and let them cool for 2 minutes before transferring them to a cooling rack.

When all the whoopie pies are cool, add frosting to one and sandwich with another. Add some more rainbow jimmies to the frosting in the middle.

Have fun and enjoy!