Preheat oven to 325º Fahrenheit.

Prepare a jelly roll pan with shortening and flour. Set aside for later.

Prepare cake batter according to the box directions.

Separate batter evenly into 3 bowls.

Add a couple drops of red food coloring to one bowl and blue to the other and mix until the colors are uniform throughout.

Transfer batter into 3 ziplock bags. Cut a small corner off of each bag.

In a diagonal pattern, squeeze strips of each color until the pan is filled. If you have batter remaining, you can go back and fill in as needed.

Gently shake the pan to even out the cake batter.

Using a toothpick, draw swirls in the batter to create a tie dye look.

Bake for 18 minutes or until the cake is set.

Remove from oven and allow to cool for 20 minutes.

Place a towel on a flat surface and sprinkle flour on it.

Flip the cake out of the pan and onto a clean towel.

Sprinkle a small amount of flour on the top side of the cake and cover it with another towel.

Starting on one end, roll the cake up with a towel on each side. Try to keep it as tight as possible.

With the cake tightly rolled, set it aside to completely cool.

When cool, gently unroll it.

To prepare frosting, add butter, vanilla and powdered sugar to bowl.

Add enough milk while whipping ingredients to reach the frosting consistency you desire.

Spread on the frosting, covering the top of the cake.

Begin rolling the cake from one end, using a towel to help guide you.

When the cake is completely rolled, wrap the towel tightly around it to help hold its form.

Place cake roll in the freezer for 4 hours.

Remove from freezer and cut into slices. Serve and enjoy.