STEP 2/6
Add vanilla extract and egg yolk, chop butter into small pieces and mix well with a whisk. Butter was in the refrigerator, so it wasn't mixed well because it was cold.
STEP 3/6
Place a paper foil on a cake pan about 20 centimeters by 20 centimeters, and then press down on 2/3 of the dough. Butter is oily, so please wear sanitary gloves and press it. Place in freezer and harden for 20-30 minutes.
STEP 4/6
2 cups blueberry cornstarch, sugar, lemon juice, I didn't have any, so I added a lemon drink and it was okay.