Preheat your oven to 200C and grease a 12-hole tart tin. Set aside.
To prepare the shortcrust pastry, place the butter and the flour together in a bowl and pop into the freezer for 10 minutes.
Whisk the egg yolks together with the salt and soured cream. Pop this into the fridge to chill.
Make the filling: cream the butter and sugar together until light and thoroughly combined. Add the egg, vanilla and cream and beat well. Fold in the currants and set aside.
Using a food processor, pulse the cold flour and butter together until it resembles coarse breadcrumbs.
Add the chilled egg yolk mixture to the flour/butter and pulse until it begins to come together to form a dough. You might need to add a few teaspoonfuls of ice cold water to help it come together.
Form the dough into a flat disc, wrap in cling film and chill for 20 minutes.
Roll the dough out to a thickness of 4 mm on a floured surface.
Using a 7.5 cm fluted cutter, cut 18 rounds from the pastry dough, rerolling the ends.
Press the rounds into the tart tin and prick the bottom with the tines of a fork, once.
Fill the tarts with the sugar/currant mixture until level with the top.
Bake in the centre of the oven for 8 minutes, then turn the heat down to 180C and bake for a further 8-10 until the pastry is golden. The filling will bubble up but it will settle back down upon cooling.
Leave the tarts in the tin for 5 minutes to cool before carefully transferring to a wire rack. Serve warm or cold.