If the butter is firm, microwave on low until it softens. To simplify the process, sift the dry ingredients (sieve is fine), preheat the oven to 170℃ (340℉), and line A baking sheet with parchment paper.
Add butter and sugar to a bowl and mix well with a spatula. Once mixed, add egg yolk and a few droplets of vanilla oil and continue mixing.
Add sifted ingredients in several batches, stirring after each addition. Once it's no longer floury and comes together, add powdered food coloring to half of the dough. Please refer to Step 8 for quantities.
Put the dough from Step 3 into a pastry bag (put the colored dough between non-colored dough), about half at a time, and pipe onto baking sheet. I'm using a transparent bag so it's easy to see. The bag is easier to handle if you don't put too much dough in at one time.
The gradation will look beautiful if you sandwich colored dough between the non-colored dough In that case, place the colored dough on a spatula, open up the pastry bag to the tip, and squeeze the dough near the tip; it's easy this way.
When creating rose shaped flowers and hearts, pipe outward from the inside and shape however you like (without difference in sizes and all rather tall), and pipe inward when creating cherry blossoms. It'll look nice this way. Feel free to sprinkle dragées, etc. if you like.
Bake in preheated oven at 170℃ (338℉) for about 10 minutes and then it's done. Don't bake too much Please be careful since they will easily crumble fresh out of the oven.
Red sweet potato powder: about 2 tablespoons. To create cherry blossom color: use about 1/2 teaspoon of red food coloring 1 to 2 g of matcha. Dissolve each with about 5 ml of water or warm water.
Story Behind this Recipe
I didn't really like the simple coloring of baked sweets in general, and came up with this recipe while I was in grade school, thinking it'll be perfect for many celebrations, such as enrollment, commencement, etc. I've been using it as a gift during many occasions for many years ever since.
Following a request I received, I listed katakuriko potato starch as a substitute ingredient for corn starch, but I changed it to cake flour since although using katakuriko starch made it easier to pipe, the grooved pattern didn't come out that well.
The grooved pattern will come out better when the dough is firm.
When using powdered food coloring, dissolve with warm water or water, and color it stronger.
If the dough seems too firm during the winter etc., soften by adding water or milk (no more than about 10 ml) or by warming it up a bit.
I made the dough in the photo by putting the colored dough between the non-colored ones. The coloring will come out nicely that way.