Purple Sweet Potato Painted Swiss Roll

The concept of painting cakes is not new but is usually done on cakes covered with fondant or some form of icing, and with artificial coloring powder (Luster dust). I bought Junko's Deco Roll Cakes sold at Kinokuniya recently and found that she uses cocoa powder or green tea powder to touch up small features on patterned swiss rolls after the cake has been rolled. Because of that, I am wondering if swiss rolls can be painted with other colors, preferably with natural ingredients and what's the effect of painting the whole cake.

I had some left over layer cake that is really bendy from my previous purple sweet potato bake so I decided to make a mini swiss roll out of it. Here's my purple sweet potato painted swiss roll with purple sweet potato cream!

First make the swiss roll by spreading some purple sweet potato cream on the layer cake, leaving about 1.5 cm from the further edge clear. Roll the cake carefully with a baking sheet below to help with shaping. Twist the ends of the baking sheet and refrigerate until firm. About 1 hour. As my portion was really small, I whipped up only about 100ml of whip topping (non-dairy whipping cream) and folded in about 26g of potato puree. I still have some leftover cream despite filling some mini chiffon donuts and this swiss roll.

If you are making a regular sized roll in a 10 x 10" square tin, simply double the recipe from my previous blog entry and bake at 170 degrees Celsius for 14 minutes. Whip up about 200ml of whipping cream (add 2 tbs of icing sugar if you are using dairy whipping cream) and fold in 60g of purple sweet potato puree.

I experimented with my own homemade paint (for colors other than brown and earthy green) by using milk powder and a bit of water as the base, with a teeny bit of gel food coloring added. Gradually add water until a desired consistency is reached and add a bit of food coloring until a desired shade is reached.

I played around with a stencil too since they come in handy for those who are artistically challenged. Use a small food brush to apply the paint on the cake. Remove the stencil carefully to avoid smudging the pattern.

I painted another flower on a stem without a stencil. Store the painted roll in an airtight container without wrapping it up and place it in the fridge until the paint dries up. I left mine in the fridge for a few hours. The milk powder based paint dries up nicely although it leaves a glossy sheen instead of the matt surface of green tea.

Here's a closer look at a slice of the mini roll...

The kids loved the mini chiffon donuts and this swiss roll so much that they were asking how come I made so few!

With love,
Phay Shing