Put the butter and icing sugar in a large bowl, mash together with a wooden spoon then beat for 1-2 mins or 2 until smooth.

Add the egg yolk, vanilla, milk, flour, cocoa and a pinch of salt, and mix again.

Tip onto your work surface and knead briefly until evenly coloured.

Wrap in cling film, pat into a disc and chill for 20 mins.

2)Heat oven to 180C/160C fan/gas 4 and line 2 baking sheets with baking parchment.

Dust the surface with a little flour, unwrap the dough and roll to the thickness of a £1 coin.

Use a 5cm cookie cutter to stamp out as many discs as you can, then re-roll the trimmings to cut out more – you should get about 35 in total.

Place on the baking sheets and bake for 10-12 mins, swapping the trays over halfway through.

Cool on a wire rack.