Grease a brownie tin with a little butter, then line the base and sides with baking parchment. Place the butter and half the white chocolate in a bowl, suspended over a pan of gently simmering water. Stir every few mins, until the butter and chocolate have melted. Remove the bowl from the pan and leave to cool for 15 mins. Heat oven to 180°C / 160°C (fan oven) / 360°F / Gas Mark 4. Combine the flour and baking powder in a bowl, with the salt.

Place the sugar and eggs in a large bowl. Using an electric hand whisk, beat the mixture until it looks thick and foamy – this will take a few mins. The egg mixture is ready when it leaves a trail from the beaters, which sits on the surface for 2 secs.

Add the vanilla to the melted chocolate and give it a good stir – don’t worry if it has separated. Pour into the whisked eggs and sugar. Use a spatula to gently fold everything together, until most of the buttery streaks have been folded in. Sieve the flour mixture into the bowl and fold together again, add the remaining chocolate chunks and stir until well combined.

Pour the mixture into your tin, smoothing it into the corners. Bake for 30-35 mins, a skewer inserted to the centre should come out with sticky crumbs, but no raw cake mixture. Cool completely in the tin – the blondies will sink in the middle as they cool, just like brownies. Cut into squares. The blondies will keep for 5 days in a sealed container.