Make the pastry by pulsing the flour, icing sugar, spices and ½ tsp fine salt together in a food processor, then add the butter and pulse again until it looks like breadcrumbs. Add the egg yolk and 1-2 tbsp cold water, and pulse until it forms a ball. Wrap and chill for 30 mins.
For the curd, mix the cornflour with a splash of clementine juice to dissolve, then tip into a pan with the remaining juice, orange juice, clementine zest, lemon juice and sugar. Bring to a simmer briefly, then remove from the heat and whisk in the butter, a few pieces at a time, then whisk in the egg yolks thoroughly. Put back on a low heat, stirring constantly until thickened, then transfer to a bowl. Cover and leave to cool at room temperature.
Roll the pastry out (in two halves if you need to) to a few millimetres thick, and line eight individual tart tins about 8-9 cm wide. Trim the edges and chill for 10 mins. Heat the oven to 200C/180C fan/gas 6.
Line the pastry cases with a piece of parchment and some baking beans, and blind-bake on a large tray for 10 mins until golden brown.
Remove the beans and bake for a further 5-8 mins until the pastry is completely cooked, and looks dry and crisp. Leave to cool in the tins.
For the meringue, put the sugar in a pan with 50ml water. Bring to the boil and simmer until it reaches 116C on a sugar thermometer. At around 110C, whip the egg whites in a stand mixer to soft peaks. With the motor still running, slowly drizzle in the sugar syrup in a thin stream, then keep whisking until the meringue cools. Spoon into a piping bag with a round nozzle about 1cm wide.
Spoon the curd into another piping bag, and pipe an even layer into the base of the pastry cases, or spoon it in, smoothing over with the back of teaspoon.
Pipe blobs of meringue over the whole curd to form peaks. Use a blowtorch to briefly cook the meringue, or grill for 30 secs-1 min until golden. Serve straightaway.