Cut the butter into small cubes. Combine flour, sugar, and butter in a mixing bowl, and beat with an electric whisk until the mixture resembles crumbs. Whisk the egg yolk into the mixture, then knead with your hands until a smooth dough forms.
Preheat the oven to 410°F (210°C). Take a small portion of the dough and press it evenly into a 2.6 inch tart mold. Trim off any excess dough from the edges with a knife and prick the bottom with a fork. Repeat these steps for the remaining eight tart shells.
Bake the tart shells for 15 minutes. Let them cool completely before removing them from the molds.
Japanese Cheese Tarts · Dinner Match Lab | Dinner Match Lab