Start by making the pastry. Place all the dry ingredients in the bowl of your food processor and give them a quick pulse. Add the butter and pulse until the mixture resembles breadcrumbs. Tip the mixture into a large mixing bowl and add the egg and water. Bring together with your hands and then gently knead the mixture a couple of times to make a smooth pastry. Wrap in cling film and place in the fridge until required.
Preheat the oven to 180C/320F/gas mark 4.
Roll out the pastry and use it to line a 26cm tart tin. Prick the base all over with a fork and bake for about 20 minutes, until turning golden. Then remove from the oven and set aside.
Put the white chocolate in a heatproof bowl with the double cream and place over a saucepan of simmering water, making sure the water doesn’t touch the bottom of the bowl. Stir until the chocolate has melted.
Leave to cool for a couple of minutes, then add the mascarpone, vanilla and eggs, and whisk very lightly until combined. Try not to get air into the mixture.
Pour two-thirds of the mixture into the pastry case and then add the raspberries, distributing them evenly. Add the rest of the mixture until you get to within 3mm of the top. Make sure the raspberries are submerged.
Place the tart tin on a baking sheet and bake for 25–30 minutes until the filling feels firm in the centre and you start to see a little cracking around the edges. Then place on a wire rack to cool completely before removing the tart from the tin.
Using a wooden spoon, hit the back of the halved pomegranate over a bowl to knock the seeds out.
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