1. Prepare all ingredients.
2. Sift the boiled egg yolks to make fine egg yolks.
3. Melt the butter at room temperature, beat it with an electric whisk until softened.
4. Add the powdered sugar to the butter two to three times, and continue to beat with an electric whisk until it turns white and expands in volume.
5. After the butter and powdered sugar have melted, add the finely cooked egg yolk and stir well.
6. Sift in corn starch and low-gluten flour, mix well, and knead into a smooth dough.
7. Divide the dough into 20 small balls and refrigerate for 30 minutes.
8. After refrigerating, take it out, put it on a baking tray, press the middle with your thumb, and just split it.
9. Preheat the oven at 170°C and bake for 20 to 30 minutes. The surrounding area is slightly golden and ready to go out. Let it cool and you can eat it.
The egg yolk must be cooked thoroughly, and it is better to handle it dry.