Rhubarb meringue pie

The day before, dehydrate the rhubarb for the garnish. Preheat the oven to 50°C (or set up a dehydrator, if you have one). Lay the finely sliced rhubarb for the garnish on a wire rack and place the rack into the oven or dehydrator. Leave to dehydrate for 8-12 hours until brittle. It will look like a lot of rhubarb for 1 tart, but they will shrink down to little crisps. Store in an airtight container for up to a week

To make the pastry, add the flour, sugar and salt to a bowl, then rub the butter into the mixture with your fingers until it becomes the texture of wet sand. Add the water a tablespoon at a time, mixing with your hands to form a dough

As soon as a uniform dough is formed, wrap in cling film and chilli the pastry in the fridge for 30 minutes

Meanwhile, prepare the meringue. Set the bowl of a stand mixer over a pan of gently simmering water (ensuring the base of the bowl doesn’t touch the water), then add the egg whites, sugar, cream of tartar and a pinch of salt

Whisk constantly, occasionally removing the bowl from the water if you think it’s getting too hot, until the mixture reaches 71°C on a temperature probe

Transfer the bowl to your stand mixer with a whisk attached. Start whisking at a low speed, increasing gradually to medium-high. Once stiff peaks form, and the bowl has cooled to room temperature, fold through the vanilla paste. Cover and set aside in the fridge

Unwrap the pastry and put it on a large piece of floured baking paper. Roll it out until around 3cm thick, then cover with another layer of baking paper. Transfer to the fridge to chill for another 15 minutes. Grease and line the tart tin

Line the tin with the pastry, then trim, finish or crimp the dough around the edges however you like. Return the tin to the fridge to chill while you preheat the oven to 180°C

Line the pastry with baking paper and fill with baking beans or raw rice. Bake for 15 minutes, then remove the beans and paper and bake for another 15 minutes until golden brown. Leave to cool completely

While the pastry cools, make the filling. Mix the gelatine and water together in a small bowl and set aside. Put the rest of the ingredients (except the whipped cream) in a saucepan and lightly simmer for 10 minutes

Leave to cool slightly, then use a stick blender to blitz everything into a smooth purée. Stir in the bloomed gelatine mixture, then pass through a fine sieve into a bowl. Fold in the whipped cream

Pour the filling into the cooled tart case, then smooth the top with a spoon or palette knife. Leave to chill and set in the fridge for at least 2 hours, or overnight

To serve, dollop the meringue on top of the tart, leaving some of the filling exposed around the edges. Use a blowtorch to toast the meringue, then sprinkle pistachios around the edges. Finish with the dehydrated rhubarb