Ingredients

• 175g/6oz butter
• plus extra for greasing
• 100g/3½oz caster sugar
• 125g/4½oz shelled hazelnuts
• ground roughly in a food processor
• 200g/7oz plain flour
• 125g/4½oz dark chocolate (70% cocoa solids)
• 125g/4½oz unsalted butter
• 2 free-range eggs
• 1 whole
• 1 yolk only
• 100g/3½oz caster sugar
• 50g/1¾oz soft brown sugar
• pinch salt
• 30g/1oz plain flour
• sifted
• ½ tsp baking powder
• 30g/1oz cocoa powder
• 240g/8½oz good-quality milk chocolate
• 300g/10½oz dark chocolate (75-80% cocoa solids)

Directions

• For the biscuit base
• preheat the oven to 150C/300F/Gas 2 and grease a 30x20cm/12x8in baking tin.
• Mix the butter and sugar together until pale and fluffy. Add the hazelnuts and flour and knead lightly to combine.
• Push the dough into the prepared tin to form an even layer. Bake for approximately 30 minutes
• or until just browning at the sides. Remove from the tin immediately and cut the biscuit into 12 x 2½cm/1in squares using a sharp knife. Set aside to cool.
• For the brownie layer
• turn the oven up to 180C/350F/Gas 4 and grease a 30x20cm/12x8in baking tin.
• In a pan set over a low heat
• melt the chocolate and butter together. In a separate bowl
• whisk the egg and egg yolk together before beating in the sugars. When the chocolate has melted
• pour it into the egg mix. Fold in the salt
• flour
• baking powder and cocoa
• then pour the mix into the prepared baking tin.
• Bake for 35 minutes
• or until the surface has set. Set aside to cool completely before cutting into 2½cm/1in squares.
• For the chocolate Chantilly
• fill a large bowl with iced water and sit a smaller bowl in it. Melt the chocolate and 200ml/7fl oz water together in a pan set over a low heat. When the chocolate has melted
• pour it into the small bowl and whisk with a handheld electric mixer until it has the texture of whipped cream. Transfer to the fridge to chill.
• For the chocolate top
• slowly melt 275g/9¾oz of the dark chocolate in a heatproof bowl set over a pan of simmering water. Grate the remaining 25g/¾oz of chocolate
• and stir into the melted chocolate until thoroughly combined. Remove the chocolate from the heat
• and pour into a 30x20cm/12x8in baking tin. Leave to cool and then place in the fridge to chill.
• Boil a kettle
• and pour the boiling water into a heatproof cup or glass. Stand a small sharp knife in the hot water
• and
• using the hot knife
• cut the chilled chocolate into 2½cm/1in squares.
• Assemble the petits fours with a layer of biscuit on the bottom
• spread on some chocolate Chantilly
• and top with the dark chocolate and finally brownie.