For the shortcrust, combine all the ingredients in a food processor and process to the consistency of breadcrumbs. Add 1 tbsp cold water if needed and pulse until a mass forms, then remove from the processor, cover in plastic wrap and chill in the fridge for 20 minutes. Roll the pastry to a 1/2cm-thick sheet and use it to line a 25cm fluted tart tin. Refrigerate a further 20 minutes. Heat your oven to 180C. Weight with pastry weights and blind bake for 30 minutes, removing the weights halfway through cooking. Cool the base to room temperature, then chill in the fridge.

For the lemon filling, mix the cornflour, lemon juice, castor sugar, egg yolks and 150ml water in a small saucepan and bring to a simmer, whisking gently until the mixture thickens. Remove from the heat and whisk in the butter. Allow to cool to room temperature.

For the raspberry filling, bring ½ cup water, the raspberry purée, castor sugar and vinegar to a simmer in a small saucepan over medium heat, and stir through the gelatine until it is fully dissolved. Remove from heat and allow to cool to room temperature.

To assemble the pie, spread the lemon filling over the base in an even layer and pour the raspberry filling on top. Chill pie for a further 2 hours until well set.

For the meringue, bring sugar and ½ a cup of water to a simmer and heat until the sugar reaches 121°C. While the sugar is heating, beat the egg whites to soft peaks in the bowl of a stand mixer. When the sugar is at the correct temperature, turn the mixer to high speed and pour the sugar into the egg whites in a thin stream. Continue to beat at high speed until the bowl of the mixer is cool. This should take about 15 minutes.

Cover the chilled pie in big spoonfuls of meringue, creating "waves" with a small palette knife, then toast the meringue with a blowtorch. Chill again and serve.