Method

• 1.
  Preheat oven to 150°C and line 2 large baking trays with baking paper.
• 2.
  Place butter and sugar in the bowl of an electric mixer and beat until pale. Add the egg yolk, vanilla and lemon zest and beat until well combined. Stir in the baking powder, flour and a pinch of salt to form a soft dough. Shape into a disc, enclose in plastic wrap and chill for 2 hours until firm. Roll out onto a lightly floured clean surface to 5mm thick. Cut out 40 biscuits, re-rolling the excess dough. Arrange on trays and bake for 20-25 minutes until firm and lightly golden. Cool completely on a wire rack.

• 3.
  Place dulce de leche in a piping bag and pipe onto half the biscuits, or use a teaspoon to add filling, then sandwich with another biscuit. Store in an airtight container for up to 2 days.