Place flour, spices, baking powder and salt in the Thermomix bowl. Mix 10 sec/speed 8. Set aside.
Place butter into Thermomix bowl. Add sugar, orange zest, vanilla and egg. Mix 1 min/Butterfly/speed 3.
Remove Butterfly. Add flour mixture. Combine 12 sec/dough setting/Interval. Finish combining with a spatula.
Roll dough out to roughly 30 x 40 cm. Place on a tray. Refrigerate until firm.
Preheat oven to 175°C. Line 2 trays with baking paper.
Cut dough into rectangles (we cut them to 2.5 cm x 4 cm). Place onto prepared trays . Bake 10-12 minutes. Cool.
To make the royal icing, place egg whites into the Thermomix bowl. Whip 4 min/37°C/Butterfly/speed 3.
Add half the icing mixture and combine 1 min/Butterfly/speed 4. Add remaining icing sugar and combine 1 min/Butterfly/speed 4. Until fully incorporated.
Divide royal icing between 4 bowls. Keep covered with a damp towel to avoid drying out.
Colour the royal icing as desired.
Place cookies on a wire rack. Set the rack over a baking paper lined tray (to catch the drips).
Pour royal icing over the cookies, in whatever way/pattern you like. Allowing it to drip off so that they're completely covered. Separate cookies before the icing sets. Let them stand at room temperature, uncovered, to set completely overnight.
In hindsight, we think that dipping them in white royal icing first, then colouring them with whichever colours you like, will be easier for full icing coverage.