Preheat oven to 190 degrees C. Lightly grease or line baking trays.
Cream the butter, sugar, eggs, egg yolk and lemon juice together until fluffy.
Combine the flour, baking powder, cinnamon, salt and nutmeg. Add the flour mixture to the creamed mixture and stir in the chopped nuts.
On a lightly floured cloth-covered board roll the dough, 1/3 at a time, to 2mm thick. Cut with a star shaped cookie cutter. Place biscuits on the prepared baking trays. Brush the tops of the biscuits with the remaining egg white, beaten until frothy.
Bake for 6 to 8 minutes.
Variations: Food colouring may be added to the egg white used to brush the tops of the biscuits. Two biscuits may be put together to form snowflakes with dabs of icing made with 1 cup icing sugar, 1/2 teaspoon vanilla and 1 to 1 1/2 tablespoons cream.