Preheat oven to 200 degrees C and grease two baking trays. In a large bowl sift together flour and cornflour then stir in the 5 tablespoons sugar and almonds.
Split the vanilla bean lengthwise and scrape out the seeds. Add the seeds to the flour mixture and mix well (if using essence, mix with the egg yolk and add later).
Rub the butter into the flour until fine crumbs or use a beater on slow. In a small bowl, beat the egg yolk. Add to the flour butter mixture and knead until a soft dough forms. Use more flour if it is too sticky.
Spoon the dough into a piping bag with a large tip and pipe 5cm ring shapes on the baking sheets, allowing some room to spread. Beat the egg white until frothy and brush on each ring, then sprinkle with white sugar.
Bake until golden, 8-10 minutes. Let cool a bit then remove biscuits to wire racks to cool completely. Dust with icing sugar.