Mix Wet Ingredients: In a large bowl, combine 150 ml sunflower oil, 180g softened butter, vanilla sugar, and a pinch of salt. Mix until smooth and creamy.

Add Egg: Beat in 1 large egg (or 2 small ones) until fully incorporated.

Incorporate Dry Ingredients: Gradually add 130g corn starch, 150g icing sugar, and 400g flour to the mixture. Stir until a smooth dough forms.

Wrap and Chill: Divide the dough into two portions. Wrap each portion in cling film and store in the fridge for 10 minutes.

Add Cocoa: Take one portion of the chilled dough and mix in 1 tablespoon of cocoa powder. Wrap again in cling film and store in the fridge for another 10 minutes.

Final Chill: Combine the plain dough and the cocoa dough into a roll or any desired shape. Wrap in cling film and store in the fridge for 30 minutes.

Preheat Oven: Preheat your oven to 190°C (375°F).

Prepare Baking Sheet: Line a baking sheet with parchment paper.

Slice and Bake: Slice the chilled dough into even pieces and place them on the prepared baking sheet. Bake for about 20 minutes or until the edges are golden brown.

Cool and Enjoy: Allow the cookies to cool on a wire rack. Enjoy your delicious butter cookies!