Melt the butter in a pan or microwave. Put the sugar and arrowroot in a large mixing bowl - add the melted butter, vanilla and 2 tbsp of milk. Use a hand-mixer to blend up until creamy. Add the milk last, starting with 2 tbsp and moving up until you have a frosting texture. Taste-test and add more sugar or vanilla if needs it.
Once the white frosting is ready, remove 1/2 cup and add 1/2 tsp beetroot juice to it and stir until combined. Want it pinker? Add a bit more beetroot juice.
Make Chocolate Frosting
To mix up the chocolate frosting, melt the butter in a waterbath or microwave at 60 seconds combined with the chocolate - don't let water touch the chocolate if you use a water bath. Put the sugar and arrowroot in a large mixing bowl - add the butter, chocolate, vanilla and 2 tbsp of milk. Blend until creamy, adding more milk to reach a frosting texture. I used chocolate chips that are 85% cacao; if you want a sweeter chocolate, use 70%.
Pipe All Frostings
Cover both frosting bowls with a soaking-wet paper towel while you finish prep.
Once you have the icings created, now let the piping begin. I used a frosting piping system by @wilton to style the frosting on my favorite cupcake recipe.