Add your first 6 ingredients to a food processor with the blade attachment fitted and give it all a whizz to fully mix together.
Dot your grated butter evenly over the flour mixture.
Pulse for about 10 pulses until the mixture resembles fine breadcrumbs. You may need to scrape down and mix around with a spatula in between to ensure equally mixed.
Add your egg yolk, vanilla bean paste and milk and pulse until the mixture just starts to clump together a little. 12 pulses should be enough.
Spread a little icing sugar out onto a clean work surface and tip your biscuit mixture out onto it.
Bring the mixture together into a large ball, knead it slightly just so it fuses together.
Flatten the ball to a depth of about 1 inch, cover with clingfilm and refrigerate for 15-20 minutes.
Heat your oven to 180°C/160°C fan/355°F/Gas mark 4
Place a piece of greaseproof paper onto the base of your baking trays.
Roll out your biscuit dough to a depth of 3mm.
Cut out 50 biscuits.
Place the biscuits onto your baking trays, leaving 1 cm between each one.
Bake for 12 minutes, or until the biscuits start to just brown at the edges and slightly on the base.
Leave to cool on the baking tray for 2 minutes, then carefully remove to a cooling rack.