Tip the flour into a bowl with the icing sugar and a good pinch of salt. Add the butter and rub in using your fingers until they resemble fine breadcrumbs. Mix the egg yolk with 1 tbsp cold water, drizzle over the flour and butter, then mix and knead briefly. Shape into a disc, wrap in cling film and chill for 30 mins.

On a floured surface, roll out the pastry until big enough to line a deep 20cm cake or tart tin, preferably one with a removable base. Drape the pastry over the tin and press it into the corners, trim the excess with some scissors but leave a 1cm overhang as the pastry will shrink while cooking. Line with a piece of scrunched-up baking parchment (to make it more pliable) and fill with baking beans or rice. Chill the tart case for 10 mins while you heat the oven to 180C/160C fan/gas 4.

Bake the pastry case for 20 mins. Remove the parchment and beans and return to the oven for another 5 mins, or until biscuit brown. Leave to cool. Now make the filling. Put the grapefruit, lemon zest and juice and the juniper berries in a pan and warm through for a few mins to help infuse the juniper flavour. In a bowl, whisk the egg, sugar and cornflour until creamy. Add the gin and mix again.

Strain the warm juice over the egg mixture, mix, then strain back into the saucepan. Set over a low heat, stirring continuously with a spatula until the mixture thickens enough to part for a second or two when stirred. Make sure you get into the corners of the pan so none of the mixture overheats and splits. Remove from the heat and mix in the butter until it has melted and the curd is smooth. Pour into the tart case, then chill for at least 3 hrs.

To make the meringue, put the egg whites, sugar, 1 tbsp water and a good pinch of salt in a large heatproof bowl. Place over a pan of simmering water, making sure the bowl doesn’t touch the hot water and whisk until thick – this should take about 5 mins. Remove from the heat and continue whisking for 3 mins until cooled slightly and really stiff.

Remove the tart from the tin. Pile the meringue on top, swirling it to create peaks and troughs. Serve as it is or use a blowtorch or grill to scorch the tips of the meringue, if you like. Leftovers will keep for up to three days.