Grate the coloured rind from the lemons using a fine grater. Melt the butter slowly in a heavy base saucepan and stir in the lemon rind and sugar. Heat gently until the sugar is fuly dissolved.
Stir one tablespoon of the hot mixture into the eggs; repeat this procedure twice more.
(This will prevent the eggs from curdling.).
Pour into the pan and heat gently, stirring constantly until the mixture thickens and coats the back of a wooden spoon. Stir in the Drambuie and heat until thick again; Do not boil! Pour into hot sterilized jars and cover.
This can be stored for up to about a month in a cool, dry dark place, or it refrigerates for up to 2-3 months very well.