Lemon Viennese Biscuits

For the lemon curd, put the lemon zest and juice, the sugar and the butter into a heatproof bowl. Sit the bowl over a pan of gently simmering water, making sure the water is not touching the bottom of the bowl. Stir the mixture every now and again until all of the butter has melted.

Lightly whisk the eggs and egg yolk and stir them into the lemon mixture. Whisk until all of the ingredients are well combined, then leave to cook for 10-13 minutes, stirring every now and again, until the mixture is creamy and thick enough to coat the back of a spoon.

Remove the lemon curd from the heat and set aside to cool, stirring occasionally as it cools. Once cooled, spoon the lemon curd into sterilised jars and seal. Keep in the fridge until ready to use.

For the biscuits, preheat the oven to 190C/170C Fan/Gas 5. Line 3 baking sheets with non-stick baking parchment. Using a 5cm/2in round cutter as a guide, draw 8 circles on each sheet of paper, spaced well apart. Turn the paper over so the pencil marks are underneath.

Measure the butter and icing sugar into a bowl and beat until pale and fluffy. Sift in the flour and cornflour and beat well, until thoroughly mixed. Spoon the mixture into a piping bag fitted with a large round nozzle. Hold the nozzle of the piping bag just above the centre of the circle and squeeze until the batter reaches the edge of the circle to leave a round biscuit with a point at the top. If you are feeling ambitious, use a star nozzle to pipe the classic whirl shape.

Bake in the centre of the oven for 13—15 minutes, until a pale golden-brown. Cool on the baking sheets for 5 minutes then carefully transfer to a wire rack to cool completely and harden.

Bake in the centre of the oven for 13—15 minutes, until a pale golden-brown. Cool on the baking sheets for 5 minutes then carefully transfer to a wire rack to cool completely and harden.

For the filling, measure the butter into a bowl and sift the icing sugar on top. Add the vanilla extract and beat with a wooden spoon or an electric whisk until very light and smooth. Spoon into a piping bag fitted with a large star nozzle.

Spoon a little lemon curd onto the flat side of 12 of the biscuits and place curd-side up on a cooling rack. Pipe the buttercream over the jam and sandwich with the remaining biscuits. Dust with icing sugar to finish.