70 g plain chocolate, roughly chopped (preferably with at least 70 per cent cocoa solids and very little sugar)

35 g golden sugar

220 g unsalted butter, chilled and diced

140 g light brown muscovado sugar

250 g plain flour

1/2 teaspoon real vanilla essence

50 g white or plain chocolate, melted, to decorate

several baking sheets, well greased

Makes about 30

Blend the chopped chocolate and caster sugar in a food processor until they from the texture of sand. Add the diced butter, muscovado sugar, flour and vanilla, then process again until the dough just comes together.

Using your hands, form the dough into about 30 walnut-sized balls. Space well apart on the baking sheets.

Bake the biscuits in a preheated oven at 180°C (350°F) Gas 4 for 10-15 minutes or until they are just firm to the touch and beginning to colour around the edges.

Remove from the oven. They are very fragile at this stage, so leave them on the sheets for 5 minutes before transferring to a wire rack to cool.

when completely cold, decorate by drizzling with the melted chocolate using either a fork or a greaseproof paper icing bag.

Leave until firm, then store in an airtight container and eat within 4 days.

Undecorated biscuits can be frozen for up to 1 month, but you may have to crisp them in a warm oven before decorating.