(from Delicious Days by Nicole Stich)
80g icing sugar
2 teaspoons matcha powder
150g cold butter
1 pinch of salt
25-50g corn starch
3 egg yolks
Sift icing sugar and matcha powder into a large bowl. Wash one of the limes with hot water and grate the zest. Cut butter into cubes and, together with the lime zest and salt, add to the sugar. With your electric hand mixer (I used the dough hook), mix until you have a bright-green smooth dough. Then, add flour and corn starch. Mix again. Then, add the eggs.
Form the dough into a flat disk and wrap into cling film. Put into the refrigerator for at least one hour. You can also leave this dough in the fridge for about 2 days.
Preheat the oven to 170°C (fan-assisted: 150°C) and line two baking trays with parchment paper. Wash the other two limes with hot water, grate the zest and grind in a mortar together with 1 tablespoon sugar. Mix with the rest of the sugar and put into a bowl.
Dust your work surface with a little flour and roll out your dough (about 5-7 millimeters). Cut out your cookies with a cookie cutter of your choice. Toss the cookies into your sugar-lime mix until they are covered with lime sugar. Align the cookies in the tray and bake in the middle of the oven. Depending on how thick the cookies are, that takes 10-15 minutes. They should be baked thoroughly, but they should not be brown around the edges. Take out of the oven and let cool on a wire rack. Keep in an air- and light-tight container.