For sweet pastry:
1. Put the flour, confectioners’ sugar, lemon zest, and salt in a bowl and add the butter. Rub it with you hands or, more easily, using a mixer fitted with the paddle attachment. Or, you can do the job in a food processor. In all cases, you need to mix the ingredients until you get a coarse bread crumb consistency, making sure there aren’t any large lumps of butter left.
2. Add the egg yolk and water and mix just until the dough comes together, being careful not to mix any longer than necessary. You might need to add a tiny amount of additional water.
3. Remove the dough from the mixing bowl and knead very lightly for a few seconds only, just to shape it into a smooth disk, 2 to 2 1/2-inches thick. Wrap in plastic wrap and chill until ready to use. The pastry will keep in the fridge for a week and for at least a month in the freezer. Thaw in the fridge overnight.
For prebaked shells:
1. Start by brushing your tartlet pans with a thin layer of melted butter, then leave to set in the fridge.
2. Meanwhile, prepare a wide, clean working surface and have ready a rolling pin and a small amount of flour. Lightly dust the work surface, place the pastry in the middle, and roll out the pastry thinly, turning it around as you go. Work quickly so it doesn’t get warm. Once the pastry is no more than 1/16 to 1/8 inch thick, cut out 6 circles using a pastry cutter or the rim of a bowl. Line the buttered pans by placing the circles inside and gently pressing them into the corners and sides. Leave to rest in the fridge for at least 30 minutes.
3. Preheat the oven to 300°F. Line each pastry shell with a circle of scrunched-up waxed paper or a piece of foil. It should come 3/8 inch above the edge of the pastry (paper muffin liners are another great solution). Fill them with rice or dried beans, then place in the oven and blind bake for about 25 minutes. By then they should have taken on a golden brown color. If they are not quite there yet, remove the beans and lining paper and continue baking for 5 to 10 minutes. Remove from the oven.
4. Keep the beans or rice and the paper holding them for future use. Remove the tart shells from the pans while they are still slightly warm and leave them to cool down completely.
For white chocolate and raspberry:
1. Crush the fresh raspberries with a fork and then pass them through a fine sieve to remove the seeds. Set the smooth coulis aside.
2. Put the white chocolate and the butter in a heatproof bowl. Heat the cream in a small saucepan and bring to a boil, watching it constantly. As soon as it comes to a boil, pour it over the chocolate and butter and stir gently with a rubber spatula. Continue until all the chocolate has melted and you are left with a smooth, shiny ganache.
3. Immediately, before the ganache begins to set, spoon 1 teaspoon jam into each shell. Carefully pour in the ganache; it should almost reach to the rim (if the ganache does begin to set, heat it gently over a pan of hot water before pouring). Be very gentle now and don’t shake the shells.
4. Spoon a tiny amount of the raspberry coulis — not more than ½ teaspoon — into the center of each tartlet. Use the tip of a knife or a skewer to swirl the coulis around. Carefully transfer the tartlets to the fridge and leave them there to set. Remove at least 30 minutes before serving.