Chocolate tart with salty caramelised walnuts

To make the pastry, put the flour, cocoa, icing sugar and ¹/2 tsp salt in a food processor and pulse briefly until combined. Add the butter and pulse for a few seconds at a time until the butter has disappeared into the flour, creating a sandy texture. Add ice-cold water, 1 tbsp at a time, pulsing in between until the pastry comes together in clumps. Don’t over-process or the pastry will become tough. Tip onto a sheet of clingfilm and draw up the sides, pressing the pastry gently into a ball. Wrap and chill for 30 minutes. The pastry also freezes brilliantly for up to 3 months if you want to make ahead.

When you are ready to make the tart, heat the oven to 180C/fan 160C/gas 4. Lightly dust a work surface with flour and roll out the pastry until it’s 3-4mm thick, turning the dough a quarter turn with every roll to keep it an even circle. Allow the pastry to rest for 10 minutes to minimise shrinkage when baked. Roll the pastry around a rolling pin and gently lift over a 25cm loose-bottomed tart tin. Unroll and press firmly into the base, making sure it gets right into the rim, letting the overhang come over the edge of the tin. Roll the rolling pin swiftly across the top to chop off the excess pastry. Use your thumb and forefinger to pinch up the pastry so it’s a couple of millimetres above the rim of the tin.

Prick the base all over with a fork and line with baking paper and baking beans. Bake for 20 minutes, then remove the paper and beans, and return it to the oven for another 10 minutes. This is the only cooking the pastry gets, so it’s important it’s crisp all the way through. Remove from the oven and cool.

While the pastry is baking, prepare the nuts. Put the egg white in a bowl and whisk for a minute or so until airy. Tip in the nuts and sugar, and stir until coated. Spread out on a baking sheet, turning the nuts so they are all flat-side down. Sprinkle over the salt and bake in the oven for 12-15 minutes or until lightly golden and crisp. Allow to cool, then roughly chop.

For the filling, put the cream, sugar, butter and vanilla in a heavy-based pan over a medium-low heat, stirring frequently until the cream is hot and the sugar and butter have melted. Turn off the heat and tip in the chopped chocolate, stirring until it’s melted and forms a thick glossy sauce. Cool for 15 minutes then pour into the cooked pastry case, giving the tin a few sharp taps against the worksurface to level it. Leave until cool then chill in the fridge for a couple of hours until set. Scatter over the roughly chopped nuts just before serving.