Sift the flour for the roll cake twice. Separate the egg yolks and whites. Bring the butter and egg whites to room temperature. Place the yogurt in a gauze-lined colander and drain the liquid for one hour.
Next, make the polka dots. In a bowl, mix the butter until soft and whisk in the powdered sugar, egg white and flour in that order.
Place the batter in two small piping bags and add the food coloring to each. Then, cut the tips off the bags.
Line a baking sheet with parchment paper and using the batter from step 3, pipe out dots of alternate colors. They should be about the size of a bean. Chill until firm in the refrigerator.
Next, make the batter for the roll cake. Using a hand mixer beat the egg whites and then add the sugar in two batches and beat until soft peaks form. Add the egg yolks and continue mixing on low speed for 1 minute. Mix in the flour using a rubber spatula by folding in from the bottom. Once the flour is incorporated, add the cream and mix until thoroughly combined.
Pour the batter from step 5 into the baking sheet from step 4 and spread evenly. Bake for 12 to 13 minutes in an oven preheated to 180℃. Once baked, place on a cooling rack with the parchment paper still attached, and let cool.
Now, make the yogurt cream. In a bowl, add the drained yogurt, cream, and sugar. Beat with a hand mixer until it forms a thick enough consistency that you could write letters in it.
Carefully remove the parchment paper from the baked sponge cake and place onto a fresh sheet of parchment paper with the browned side up. Spread the cream from step 7 over the entire cake. Line pineapple rings which have been cut into 8 pieces across the cake. Start to roll the cake from bottom.
Place the cake with the rolled edge facing down and allow it to rest in the refrigerator for at least 1 hour.
Remove the cake from the parchment paper, taking care not to disturb the polka-dot pattern. Cut into slices however thick you'd like them and enjoy.
This is what a cross section of the cake looks like Pineapple and yogurt cream really go well together.
Story Behind this Recipe
I've made cakes with chocolate polka dots before, but this time I wanted to challenge myself with a butter decoration technique I'd recently learned. In the spirit of summer, I combined the tartness of canned pineapple with the refreshing taste of yogurt cream. Refreshing and delicious!
I bought liquid food coloring at Cuoca. If you use powdered food coloring, dissolve it in a very small amount of water. Although it may seem like it somehow takes a long time to assemble this cake, I don't think each individual step is very difficult Please take care that you remove the parchment paper carefully and gently. Don't pull off the little polka dots you so carefully made!