150 g unsalted butter, chopped, at room temperature
165 g ( ¾ cup) caster sugar
2 egg yolks
60 ml (¼ cup) milk
1 tsp vanilla extract
550 g plain flour
1 tsp baking powder
Preheat oven to 200°C. Using an electric mixer, beat butter and sugar for 4 minutes or until pale and fluffy. One by one, add 2 eggs and 1 egg yolk, beating well after each addition, until well combined.
Combine milk and vanilla in a small jug. In another bowl, sift flour and baking powder with a pinch of salt. Using an electric mixer, add milk mixture alternating with flour mixture until a smooth, soft dough forms; don’t overwork the mixture.
Turn dough out onto a lightly floured work surface. Using 1½ tbsp dough for each biscuit, shape into 40 x 20 cm logs. Fold each log in half, then twist together, pressing the ends together to seal.
Place biscuits on a lined oven tray, spaced 2cm apart. Lightly whisk remaining egg yolk with 1 tsp water. Brush biscuits with the egg wash and bake for 12 minutes or until golden. The biscuits will keep in an airtight container for up to 10 days.