Stir butter and sugar in a medium saucepan over medium heat for 2 minutes or until butter melts and combines with sugar. Add cream, milk and vanilla bean, stir until mixture comes to a simmer.

Whisk egg yolks in a medium bowl. Gradually add the warm milk mixture, whisking until combined. Return mixture to pan, cook over low heat, stirring continuously, until mixture thickens enough to coat the back of the spoon. Do not allow to boil.

Strain mixture into a medium bowl, discard vanilla bean. Cover surface of custard directly with plastic wrap, cool to room temperature. Refrigerate until chilled.

Spoon custard into an ice-cream machine. Following manufacturer's directions, churn until frozen. Grease a 19cm x 29cm slice pan, line base and sides with baking paper. Stir almonds into ice-cream. Spoon mixture into the slice pan. Cover, freeze 3 hours or overnight.

Cut a 7.5cm (3-inch) triangle from thick cardboard to use as a template for biscuits and ice-cream.

Process butter, sugar, flours and cocoa until mixture is crumbly. Add egg yolk, extract and the water, process until ingredients just come together. Wrap dough in plastic wrap, refrigerate 30 minutes.

Roll pastry between sheets of baking paper until 4mm (¼-inch) thick. Using the cardboard template, cut 24 triangles from pastry. Re-roll scraps if necessary. Place triangles on two baking-paper-lined oven trays. Refrigerate 30 minutes.

Preheat oven to 160°C (180°C fan forced). Bake biscuits for 12 minutes or until crisp. Stand on trays 5 minutes before transferring to wire racks to cool.

Using the cardboard template, cut 12 triangles from the ice-cream. Sandwich ice-cream between two biscuits. Freeze sandwiches for 15 minutes or until firm. Serve immediately, dusted with dutch cocoa.