Pre-heat the oven to 200 °C.
Whisk the butter and icing sugar until fluffy. Add the eggs one at a time. Mix in the other ingredients.
Roll out the dough into three bars on a baking sheet lined with parchment paper.
Bake the bars in the middle of the oven for about 15 minutes. Cut them into pieces, around 3-4 cm in size. Bake the pieces at 200 °C for a further 6 minutes or so on each side until crisp.
Store in a container with a tight-fitting lid.
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