230g plain flour, plus extra for dusting
150g firm unsalted butter, cut into small pieces
115g icing sugar, sifted
a pinch of salt
3 large egg yolks
½ teaspoon vanilla extract
2-3 teaspoons cold water
2 egg yolks beaten together with 1 tablespoon caster sugar, to glaze
Place the flour, butter, icing sugar and salt into a mixing bowl. Rub together until it resembles breadcrumbs. Add the egg yolks and vanilla extract and mix well. Add the water, a teaspoon at a time, and bring the mixture together; you may not need all the water.
On a lightly floured surface, knead gently to form a smooth ball of dough. Wrap in clingfilm and place in the fridge for at least 30 minutes.
Line two trays with parchment paper and preheat your oven to 180°C/Gas 4.
On a lightly floured surface, roll out the dough to 5mm thick. Using a 7cm fluted cutter, stamp out 25 to 30 rounds. You will need to reroll the trimmings. Place the biscuits onto the prepared trays, brush with the egg yolk glaze, place in the fridge to rest for 30 minutes.
Just before baking, brush with the egg glaze again. Use a fork and press gently to draw wavy lines through the egg wash and the surface of the biscuit. Bake for 12 to 14 minutes until golden brown and shiny on the surface. The biscuits will be soft whilst warm, so leave on the tray for a few minutes until they have set, then transfer to a wire rack to cool.