Melt the chocolate and combine with soured cream. Stir in 125g chocolate biscuit crumbs. Cover and chill until firm.
Roll by level tablespoonfuls into balls. Mould to a slight point at one end (the nose) to form mice.
Roll each mouse in icing sugar (for white mice), and in chocolate biscuit crumbs (for dark mice). On each mouse, place dragées in appropriate spot for eyes, almond flakes for ears and a liquorice string for the tail.