Add butter and sugar in a bowl of a stand mixer and mix for 2 minutes. Add egg and mix, and then add cake flour, vanilla and lemon zest. Mix well. Form the cookie dough into a log and chill for 30 minutes.

After finishing step 4 in Japanese Basic Bread Recipe (making 8 small dough balls and letting rest for 15 minutes)

Cut the chilled cookie log into 8 pieces, and roll out into 5" (12cm) flat rounds. Then cover the bread dough balls with the cookie dough rounds. Roll the cookie surface in sugar, and score with a knife in a grid pattern. Place on the baking sheet with parchment paper and let rise for 45-60 minutes.

Bake at 400F for 9-10 minutes. Take out of the oven and let cool.