• 125 g (4 oz) butter
• 25 g (1 oz) plain chocolate, broken up
• 1 teaspoon instant coffee
• 75 g (3 oz) soft dark brown sugar
• 1 teaspoon vanilla essence
• 1 egg, beaten lightly
• 25 g (1 oz) plain flour
• ½ teaspoon salt
• 50 g (2 oz) skinned hazelnuts, toasted and chopped

Preheat the oven to 190°C, 375°F, Gas Mark 5. Butter a 25 × 30 cm (10 × 12 in) Swiss roll tin. Melt the butter and chocolate together, over the lowest possible heat, stirring. Add the instant coffee and stir to dissolve. Remove from the heat and stir in the sugar and vanilla essence; then the egg. Sift in the flour and salt and mix until smooth.

Pour into the tin and spread evenly. Sprinkle all over with the chopped hazel nuts. Bake for 12-15 minutes, turning the tin round halfway through. The biscuit mixture should firm up, but still seem soft – the biscuits will crisp up on top and round the edges as they cool.

Cut at once into squares or oblongs. Cool in the tin for 1-2 minutes, then transfer to a wire rack to cool completely.