Make the pastry in a food processor by pulsing the sugar and butter together until full combined; add the egg yolks, vanilla and tonic water and pulse again until fully incorporated; add the flour and pinch of salt and pulse again until the flour is fully incorporated and the pastry looks smooth; take out of the processor and bring together with your hands; shape into a flat disc and chill in the fridge for at least 30 minutes
Make the curd by whisking the lemon zest and juice, gin, sugar, eggs and yolks together in a large heatproof bowl; add the juniper berries and butter and place the bowl over a pan of gently simmering water, making sure that the bowl does not touch the water; once the butter has melted, let the curd cook for 8-10 minutes, stirring regularly until it is thick enough to coat the back of a spoon; meanwhile, soak the gelatine in a small bowl of cold water for a few minutes to soften
Once the curd has thickened, remove the bowl from the pan and squeeze out the excess water from the gelatine and stir into the warm curd; when the gelatine has dissolved, strain the curd into a large bowl to remove the juniper berries; cover the surface directly with clingfilm and allow to cool
Heavily grease and base-line a deep 23cm tart tin and roll out the pastry on a lightly floured surface about 3mm thick; line the tart tin with the pastry; cover and chill for another 30 minutes; preheat the oven to 180C/Gas4 and bake the tart case blind; set aside to cool; spread the lemon curd into the pastry case and chill for at least 4 hours or overnight, to firm up, covering once the top has set
10 servings