Prepare the mould. Break the chocolate into pieces for the chocolate fudge mixture. Melt with butter and half condensed milk over low heat while stirring. Smooth the mixture in the mould, chill for 10-15 minutes.
For the peanut fudge mass, roughly chop the nuts. Melt the rest of the condensed milk with peanut butter at low heat while stirring. Fold in the nuts. Spread on the chocolate fudge mixture and chill for at least 6 hours.
Lift fudge out of the mould and cut into cubes.