Chop the soap into small chunks, around 2cm square.
Melt in a double saucepan.
Alternativately melt the base in a microwave for about 3 minutes, in 30 second blasts until melted throughout.
Grate the rind of the fruit on the coarse side of the grater.
Once your soap base has melted, add the grated rinds as well as the essential oil (at a rate of 2.5mL per Kg). Mix gently to avoid bubbles.
Once mixed, pour the soap into your mould - if any bubbles are present a light spray with rubbing alcohol can help to remove them.
Let your soap cool then pop out of the mould. Resist the urge to touch it! Clear soap base is not very forgiving when it comes to fingerprints.