Method

1. First, make the jam. Tip the raspberries and sugar into a saucepan and cook over a low-medium heat, stirring occasionally until the sugar has dissolved and the raspberries have broken down. Turn the heat up to medium-high and bring the mixture to the boil. Cook for 4-5 mins until thick and jammy. Pass through a sieve into a bowl and leave to cool completely. Chill until needed (it will thicken further as it chills).

2. To make the biscuits, beat the butter, sugar and vanilla together in a large bowl using an electric whisk until pale and fluffy. Beat in the egg yolk, followed by the flours and a pinch of salt. If the dough is too stiff, you can mix in the milk, ½ tbsp at a time. Use your hands to bring the dough together into a disc, then wrap in baking parchment and chill for 30 mins to firm up.

3. Divide the chilled dough into two equal pieces and roll out each piece on a lightly floured surface (or between two sheets of baking parchment) until it's roughly 3mm thick. Use a 5-6cm round cookie cutter to stamp out circles from both pieces (you should get about 24 in total). Stamp a small hole out of the centre of half of the biscuits using an apple corer, the base of a piping nozzle or a small heart-shaped cutter. Re-roll the trimmings to stamp out more biscuits, if needed. Arrange the biscuits on baking trays lined with baking parchment, spacing them well apart. Chill on the trays for 20 mins (or freeze for 10 mins) to firm up.

4. Heat the oven to 170C/150C fan/gas 3. Bake the biscuits for 10-12 mins, or until the edges are slightly golden. Leave to cool completely on the trays.

5. For the buttercream, beat the butter and vanilla together using an electric whisk until pale. Sift in the icing sugar and beat until pale and fluffy.

6. To assemble, spread a thin layer of buttercream over the whole biscuits. Spoon over the jam and gently smooth the surface. Dust the remaining biscuits with icing sugar, then sandwich on top, sugar-side up. Will keep in an airtight container for up to five days.