Tip the flour onto a work surface and make a well in the centre. Add the salt.
Dice the cold butter and place in the middle of the flour. Slide in the egg yolk.
Rub everything from the outside to the inside to form crumbs.
Quickly knead the crumbs into a smooth dough.
Shape the dough into a ball and place in the fridge wrapped in cling film for 30 minutes.
Preheat the oven to 200°C (180°C fan, gas 6). Butter the tart tin and sprinkle with flour. Roll out the dough between two layers of cling film until slightly larger than the tin.
Remove the top sheet of cling film from the dough, turn it over and place in the tin. Remove the second layer of film and use the dough to line the tin. Press into the edge well and cut off any excess dough.
Grate the cheese and whisk with the eggs, sour cream, a little salt, pepper and nutmeg. Pour onto the dough base, spread out evenly and bake in the oven for 45 minutes until golden brown.