Preheat the oven to 180°C/gas mark 4

Sift the cocoa powder and flour together in a large bowl, then stir in the sea salt and caster sugar. Add the softened butter by the spoonful and using a fork, followed by your fingers, work the butter through the dry mix until you’re left with a sandy rubble

Pour in the milk, then using the fork, bring the mixture together into clumps. Dive in again with your hands and gently press the dough together. It will seem crumbly, but you don’t want to overwork it

Tip the dough out onto a clean dry surface, and with a very lightly floured rolling pin, roll the dough out to the thickness of just under two £1 coins

Use a round cookie cutter (anything from 4cm–6.5cm depending on how big you want the biscuits) to stamp out rounds and transfer them to a baking sheet lined with greaseproof paper. Reroll and stamp out the leftover dough until you’ve used it all up

Place the baking sheet in the fridge to let the biscuits chill down for 20 minutes, before transferring the tray into the oven to bake. If you’ve made slightly larger 6.5cm biscuits, leave them in for 15 minutes, or if you’re on the smaller end at 4cm, take them out after 12. Transfer to a wire rack to cool down completely

While the biscuits are cooking, beat the peanut butter, softened butter, icing sugar and salt together and set aside

When the biscuits are completely cool, sandwich together with the buttercream and leave to set at room temperature for an hour before tucking in. The filling will continue to set the longer they sit. Store in an airtight tin for 2–3 days