Preheat the oven to 170°C (150°C Fan, Gas Mark 3). Grease and line an 18cm (7 inch) square cake tin. Break 100g (3 ½ oz) White Chocolate into pieces and place in a heatproof bowl with the butter. Put the bowl over a saucepan of gently simmering water. Leave to melt then remove from the water and cool for 10 minutes.

Using a large sharp knife, cut 175g White Chocolate (6oz) into small chunks. Beat the eggs and sugar into the melted Chocolate. Sieve the flour and Baking Powder on top, add the ground almonds and Lemon Extract, and carefully fold into the mixture along with the White Chocolate pieces until well combined.

Transfer to the prepared tin and smooth over the top. Bake in the oven for 25 minutes until risen, lightly golden and lightly crusty on top – the mixture should be slightly soft underneath. Leave to cool completely in the tin - the cake will sink slightly on cooling. Remove from the tin, and wrap and store for 24 hours to allow the texture to develop before serving.

To serve, cut into 12 equal portions. Melt the remaining Chocolate as above and spoon into a small piping bag fitted with a fine plain nozzle. Drizzle White Chocolate over each piece and leave to set for a few minutes before serving.