Heat the oven to 170 C / 340 F. Line a rimmed baking sheet with parchment paper.

In a large mixing bowl, beat the softened butter and powdered sugar together with a spatula until pale and smooth, about 2 minutes.

Add the egg yolk and vanilla extract and mix until fully combined.

Sift the flour, matcha powder, and salt together directly into the bowl. Fold with the spatula until a soft, cohesive dough forms with no dry streaks.

Turn the dough out onto a lightly floured surface or between two sheets of parchment. Roll to about 6 mm / 1/4 inch thickness.

Cut into rounds or desired shapes with a cookie cutter or sharp knife. Re-roll scraps once and cut again.

Arrange cookies on the prepared baking sheet about 2 cm apart. If the dough feels warm and soft, refrigerate the cut cookies for 10 minutes before baking.

Bake for 12 to 14 minutes until the edges are just barely pale gold. The centers will look slightly underdone.

Remove from the oven and let cookies cool on the pan for 10 minutes before transferring. They firm up as they cool.