Bourbon biscuits and rhubarb liqueur ice cream

For the ice cream, whisk the egg yolks and sugar using electric beaters until pale and fluffy. Put the cream, milk and vanilla extract into a pan and bring slowly to a simmer.

Pour the hot cream mixture over the eggs, while whisking. Transfer back to the pan and cook over a low heat, stirring until it coats the back of a spoon or reads 86C on a digital thermometer. Pour into a bowl, cover the surface with clingfilm and cool completely, then add the rhubarb liqueur. (You can make this the day before, if you like.) Pour into an ice cream machine and churn until frozen.

For the biscuits, use electric beaters to cream the butter and both sugars until light and fluffy. Add the egg and remaining dry ingredients, then beat until a stiff dough forms. Wrap and chill in the fridge for 30 minutes.

Heat the oven to 180C/fan 160C/gas 4. Roll the dough out on a lightly floured work surface to a large rectangle the thickness of a pound coin and then cut into 6cm x 4cm rectangles. Put onto several baking-paper-lined trays and prick neatly with a fork. Chill for 15 minutes, then bake for 8-10 minutes or until firm. Sprinkle with the 1 tbsp caster sugar, then cool on the trays.

Put the rhubarb into a pan with the sugar and lemon juice. Cook slowly for 10-15 minutes until broken down, then blitz in a food processor until smooth.

For the filling, melt the chocolate and then cool. Beat the butter and sugars with an electric whisk until soft and fluffy, then add the milk, cocoa and melted chocolate. Mix well and put into a piping bag. Pipe the filling onto 4 of the biscuits, then sandwich with 4 more.

To serve, spoon the rhubarb purée onto 4 plates, add two of the bourbon biscuits and a scoop of the ice cream.