Cut a sheet of foam board to be slightly bigger then the bottle.
Place some clay on top so it's about roughly 1cm thick.
Place the bottle on top and making sure it's straight then start to build up the clay around the sides so it's only half way up make sure it's clean and straight.
Place a little piece of clay on top where there’s room so it's slightly raised, this will make it easier for the two pieces of silicon to hold together after.
Make a box to fit around the bottle and make sure it's well sealed with tape. Clean the insides so the clay is tight to the edges so no silicon can leak.
Spray the mould with a silicon release spray then pour in the silicon.
Leave the silicon to harden - best overnight, but all silicone are different.
Remove the box and turn over the mould, remove the clay and clean the bottle and silicon so there is no clay residue left.
Build another box around the silicon and spray with release spray again.
Fill with silicon and leave again to dry.
When dry remove the box and pile back the silicon and clean.
Fill one half with chocolate and place the other part of the mould on top and seal with tape then keep rotating for 2 minutes or so so that the chocolate will fill in to the gaps. Refrigerate and remove the bottle.