Place a Pyrex or metal bowl on top of a saucepan that has a small amount of water in it. Bring the water to a slow simmer over a moderate heat then turn the heat down to low.
Grate or finely slice the cacao butter and add to the bowl. The cacao butter will start to melt straight away – use a whisk to stir it around as it melts.
Once the cacao butter has melted, add the sifted icing sugar (or honey) a little at a time and stir well until the sugar is fully incorporated.
Now add the milk powder and stir well. Then add the cacao powder (or cocoa) and stir well once again. Finally add the vanilla bean paste (if using) and the salt. Stir until well combined.
Turn the heat off, but keep the chocolate over the saucepan to keep it warm while you layer the chocolate.
Using a small teaspoon, add a small amount of chocolate mixture into chocolate moulds, tap the moulds to level out the chocolate if needed, then put into the freezer to harden (it only takes about 10-15 minutes).
Take out the hardened chocolate and, using a small teaspoon, add small amounts of peanut butter over top, keeping it centred as much as possible. Place in the freezer to firm up for another 10-15 minutes.
Take out of the freezer and spoon more chocolate over top of the peanut butter to fill the mould cavity, tapping lightly to level the chocolate if needed. Place in the freezer to harden.
Take out of the freezer, allow to come to room temperature, and serve. Store extras in fridge or freezer to keep firm and shiny.