Put 6 tbsp. of grated castile soap and some water in a heatproof bowl and place over a saucepan of boiling water. When the soap has melted, stir in 5 tbsp glyverine. Remove from heat and stir in 4 drops of lavender oil.
If desired, stir in a few drops of natural food colouring to colour the soap. When cool, pour into clean bottles and seal with corks.