Pre-heat the oven to 175'C.
Dice the butter and keep at room temperature. The butter should be pliable: soft enough to poke into, but not so soft that it cannot keep its shape.
Split the vanilla bean lengthwise, and scrape out the seeds.
Combine the plain flour, cornstarch and icing sugar, making sure that no lumps remain. Sieve the dry ingredients if necessary.
Toss the diced butter into the dry ingredients, and rub the ingredients until you obtain a fine breadcrumb-like texture. If your hands tend to be warm, use two forks/a potato masher/pastry knife to combine the ingredients.
Once the mix starts resembling ground almonds, start to gently knead together to obtain a smooth dough. Alternatively, you can use a food processor on the pulse setting or a stand mixer with a paddle.
Scrape the dough into a pipiing bag, and pipe out the biscuits into the desired shapes onto a paper-lined baking sheet.
If prefered, the dough can be rolled into a sausage and left to chill until needed. Slice the dough into biscuits before baking.
Bake until just begining to turn golden brown around the edges, about 10-12 minutes.
Leave to cool down before removing the biscuits from the baking tray.
Serve warm or keep in an airtight container until readuy to serve.
«Sable biscuits are at their best when simple, but they can be decorated with sprinkles before baking or with royal icing after they've cooled down.»