Line 2 cookie trays with baking paper and set aside.
Place sugar, zest and semolina into Thermomix bowl and mill 10 sec/speed 10.
Add butter and mix 20 sec/speed 5.
Add remaining ingredients and mix 10-15 sec/speed 5. Tip onto floured Silpat mat and press into a disc. Wrap and refrigerate for 30 minutes.
Preheat oven to 160ºC.
Roll into long sausage shape and cut into rounds. Bake for 35 minutes until golden around edges. Dust with icing sugar whilst still warm.