Preheat your oven to 170°C (340°F) for 10 minutes with both upper and lower heat for even baking.

Ensure butter is softened (pressable with a finger) but not melted.

Bring the egg to room temperature before adding it to the butter.

In a large bowl, mix the softened butter with 60g powdered sugar using a spatula until smooth and slightly fluffy.

Add the egg in 3 portions, beating well after each addition until fully incorporated to prevent separation.

Sift in cake flour and matcha powder, then fold gently with a spatula until no dry flour remains. Press lightly by hand to form a smooth dough—avoid overmixing.

Divide the dough into 40g portions and roll into smooth balls. Place on a parchment-lined baking sheet, spacing 5cm apart.

Use your finger or a small tool to make a 1cm deep indentation in the center of each ball (do not poke through the bottom).

Bake in the middle rack at 170°C (340°F) for 20 minutes until edges are lightly golden and surfaces are set.

Cool completely for 30 minutes before filling; this allows cookies to crisp slightly.

Mix mascarpone and 10g powdered sugar until smooth and lump-free.

Add heavy cream and mix until thick, smooth, and slightly flowy. Adjust consistency:

Too runny → chill 10 minutes.

Too thick → add 5g more cream.

Transfer to a piping bag for assembly.

Pipe the filling into the cookie center until full; a slight overflow looks visually appealing.

Optionally dust lightly with matcha powder for decoration.