Heat the oven to 180C/160C fan/gas 4. Line a large baking tray with baking parchment. Tip the butter and sugar into a bowl and beat, using electric beaters or a stand mixer, for 3-5 mins, until really soft and creamy. Pour in the vanilla and beat for 20 seconds, until well incorporated. Add the flour and stir together using a spatula. Once almost mixed in, bring together with your hands.

Divide the dough into 18-20 balls, weighing roughly 15g each, and roll into balls. Put the balls on the prepared baking trays, well spaced apart. Using a fork dipped in water, gently press down to flatten the balls, and leave a fork indent. Bake for 12-15 mins, until pale golden around the edges. Leave to cool completely on the trays.

To cover the biscuits with chocolate, melt the chocolate in a heatproof bowl, set over a pan of gently simmering water. Line a baking tray with baking parchment. Once the biscuits have cooled, dip half of each biscuit into the chocolate, then carefully transfer to the rack to set.