Heat the oven to 190C/170C fan/gas 5. Tip the butter, sugars and vanilla into a bowl and beat with an electric whisk until pale and fluffy. Beat in the egg. Add the flour, bicarb and a pinch of salt, and mix everything together with a spatula.

Break off golf-ball-sized lumps of dough (about 65g each) and press into the holes of a 12-hole muffin tin, ensuring it comes up the sides – if you’re using a deep muffin tin, the dough should come about halfway up the side of each hole. Bake for 15 mins until golden. The dough will sink as it bakes, so leave until cool enough to handle, then press it up the sides of the holes again. Leave to cool completely.

Break the chocolate into a heatproof bowl and melt until smooth in the microwave in 20-second bursts, or set over a pan of barely simmering water ensuring the bowl doesn’t touch the water. Remove the cookie cups from the tin (you may need a cutlery knife to help you do this). Spoon 1 tsp nut butter into the centre of each, then cover with the melted chocolate. Leave to cool until the chocolate sets, about 1 hr. Will keep in an airtight container for up to five days.