Blackberry and hazelnut meringue roulade
75g hazelnuts, lightly toasted and cooled
175g golden caster sugar, plus 2tbsp extra
1tsp cornflour oil, for greasing
5 egg whites
1tsp pure vanilla extract
1tsp white balsamic vinegar 2tbsp golden icing sugar
For the filling and topping
½tsp vanilla extract
1tsp golden icing sugar, plus extra to dust
75ml double cream 250g-300g blackberries, plus extra to serve (optional)
23cm x 32cm Swiss-roll baking tin
Put 25g of the cooled nuts in a mini-processor and grind (not too finely) and reserve for the filling. Put the remaining 50g hazelnuts, the 2tbsp golden caster sugar and cornflour into the processor and whizz to a very fine powder.
Using a piece of kitchen paper, rub the inside of your tin with oil and line with baking paper so it comes up to the sides of the tin by around 1cm.
Preheat the oven to 160C/ 320F/Gas 3. Put the egg whites in a large bowl and whisk (use electric hand beaters) until peaks form. Add the sugar a little at a time, whisking between each addition until a thick, shiny meringue forms. Fold through the vanilla and white balsamic vinegar followed by the finely ground hazelnut, sugar and cornflour mixture.
Spoon into the prepared tin and smooth the mixture evenly to the edges. Bake for 28-30 minutes until golden and set. Meanwhile, put a large sheet of baking paper on a dry surface and dust over the golden icing sugar.
Take the meringue out of the oven and leave to cool for around 5 minutes. Turn the meringue out of the tin, upside down onto the dusted baking paper and leave for a few minutes before peeling off the paper. Leave to cool completely.
To make the filling, put the mascarpone in a bowl with the vanilla extract, sift over the golden icing sugar and mix well. Add the double cream a little at a time and mix until smooth.
When the meringue is cold, spread over the filling using a palette knife and dot with the blackberries. Roll into a roulade using the paper to guide and keep an even shape. Chill for up to a few hours or eat sooner. To serve, dust with the remaining golden icing sugar and slice thickly. Scatter with a few extra blackberries, if desired.