Line a 12 hole muffin tin with paper cupcake cases or use silicone ones.
Beat the peanut butter, honey, (icing sugar if using) vanilla extract and salt together in a small bowl.
Divide the mixture into 12 and either roll into balls then flatten to nearly the size of the cupcake case bottoms or squash into suitably sized silicone moulds.
Place on a tray lined with baking parchment (unless using a silicone mould) and freeze for 15 minutes or so whilst you get on with melting the chocolate.
Either temper the chocolate according to your preferred method or following Kate's instructions or melt it using the following method.
Melt the milk chocolate and half the dark chocolate gently in a bowl placed over barely simmering water, ensuring the bowl doesn't actually touch the water. Remove from the heat and add the rest of the dark chocolate. Leave to melt for a few minutes, then stir until just combined.
Swirl a loaded teaspoon of chocolate around the bases of each cupcake case to cover.
Place a frozen peanut butter disk on top of the chocolate.
Cover with the remaining chocolate (about 2 tsp each) and tap to settle and level the chocolate.
Sprinkle with a few of the crushed cocoa nibs and leave to set - about an hour depending on room temperature.