Sift flour, icing sugar and cinnamon together; rub in butter until mixture resembles breadcrumbs. Mix in ground hazelnuts and lemon rind, add egg yolk and combine well to make a dough (your hand is best for this). Knead dough lightly until smooth and chill 30 minutes. Roll out dough on a lightly floured surface to 3mm thickness and cut into rounds or other shapes with a 5cm cutter. Place rounds on lightly greased oven trays and bake in a moderate oven 180C (350F) for 10-15 minutes or until lightly colored. Ease biscuits with a spatula, cool three minutes on trays then remove to a wire rack. Melt chocolate over hot water and spread a little on each cooled biscuit. Top with a sprinkling of chopped hazelnuts or a hazelnut half if desired.
Note: This is a very soft dough. If hard to handle, roll out between two sheets of plastic film and chill before cutting out biscuits. 98