Put the butter and honey in a saucepan with the treacle, sugar and zest. Place over a low heat, stirring occasionally until melted. Cool for 10 minutes.
While still warm, sift in the flour, cocoa, spices, bicarbonate of soda and salt. Stir in the almonds and egg yolk and mix to form a dough.
Leave the Lebkuchen on the trays for 10 minutes to firm up before transferring them to a cooling rack. Let cool completely before decorating.
Find the centre point of each biscuit and pipe 5 straight lines from the centre to the end of each star point. Pipe shorter lines, swirls and dots to decorate them like snowflakes.