To make the pastry, sift the flour into a bowl with the salt, then rub in the butter until the mixture resembles breadcrumbs. Add the egg yolk and 1 tablespoon of chilled water and mix to form a dough. Chill for 20 minutes. Preheat the oven to Gas Mark 7, 220°C, fan 200°C. Roll out the pastry to line individual tart tins, prick the bottom of the cases and chill for a further 10 minutes before baking. Blind bake for 10 minutes. For the tatin, heat the butter and sugar in a small ovenproof pan. When the sugar and butter begins to caramelise, add the apple and a few thyme leaves and stir to coat fruit in the mixture. Place the caramelised apple mixture in the pastry cases and return to the oven for 5-10 minutes until the apple is soft. For the coulis, purée the raspberries and push through a fine sieve. Gently heat the purée in a pan with the sugar until it dissolves. To serve, pour a little single cream over the tarts, decorate with a sprig of thyme, and drizzle the raspberry coulis around the plate.