Make the pastry by tipping all the ingredients, except the yolk, into a food processor and pulsing to the texture of breadcrumbs. Add the yolk, then pulse until it all comes together to form a soft pastry. The pastry will be too soft to roll out, so press it evenly into a loose-based 25cm tart tin until the pastry comes up above the edges of the tin. Rest in the freezer for at least 20 mins.
Heat oven to 190C/fan 170C/gas 5. Line the tart case with baking parchment and baking beans, then place on a baking sheet and bake for 20 mins until the edges are starting to brown. Remove the beans and paper, then continue to cook for 10 mins until biscuity. Leave to cool, trim the edges with a knife, then carefully remove from the tart tin.
To make the filling, whisk the crème fraîche with the sugar, vanilla, lemon juice and zest until thick. Spread over the bottom of the tart case, then meticulously place the raspberries on top in concentric circles. Meanwhile, heat up jam in the microwave or in a pan with 2tbsp water until bubbling. Push the glaze through a sieve into a bowl, then paint it over the raspberries with a pastry brush. Bring the whole tart to the table and serve in slices.