A soft squidgy middle is unique to brownies and is achieved by whisking the eggs and sugar until mousse-like, then baking only until the top is crisp. Take care not to overcook them or you will lose this unctuous texture and they will become cake-like.

Preheat the oven to 180°C/350°F/gas mark 4. Line a 20 cm square cake tin with greaseproof paper.
Melt the chocolate and butter in a bowl resting over a pan of simmering water, making sure the base doesn’t touch the water.
In a large bowl, beat together the eggs and sugar until thick and foamy – this will take around 8-10 minutes.
Add the melted chocolate mixture, flour, nuts and white chocolate and carefully fold everything together. Spoon into the prepared tin and bake for 25 minutes until the top is set and gives a little when pressed lightly. Cool in the tin.
Dust with cocoa, then cut into squares and serve. Any leftovers will keep well in an airtight container for up to five days.

Preheat the oven to 180°C/350°F/gas mark 4. Line a 20 cm square cake tin with greaseproof paper.
Melt the chocolate and butter in a bowl resting over a pan of simmering water, making sure the base doesn’t touch the water.
In a large bowl, beat together the eggs and sugar until thick and foamy – this will take around 8-10 minutes.
Add the melted chocolate mixture, flour, nuts and white chocolate and carefully fold everything together. Spoon into the prepared tin and bake for 25 minutes until the top is set and gives a little when pressed lightly. Cool in the tin.
Dust with cocoa, then cut into squares and serve. Any leftovers will keep well in an airtight container for up to five days.