Leek and Potato Tart with Crème Fraîche Custard

Shortcrust

• 200 g Plain flour
• ½ tsp Fine sea salt
• 125 g Unsalted butter, cold
• 1 Egg
• 2 tbsp Water, cold

Filling

• 450 g New potatoes
• 2 medium Leek
• 20 g Unsalted butter
• 1 tbsp Dijon mustard
• 6 sprigs Fresh thyme
• ½ tsp Black pepper

Custard

• 2 Egg
• 150 ml Whole milk
• 150 g Crème fraiche
• ¼ tsp Fine sea salt

1. Tip the flour and salt into a bowl, then rub in the cold butter until it looks like fine crumbs. Beat 1 egg with the cold water, add to the bowl and bring together into a smooth dough without overworking. Flatten into a disc and chill for 30 minutes.
2. Heat the oven to 190°C (375°F). Roll the pastry on a lightly floured surface to line a 23 cm tart tin, pressing it neatly into the corners. Chill for 10 minutes while the oven heats.
3. Prick the base all over with a fork, then bake for 15 minutes until the edges look set and just starting to colour. If the base puffs, press it down gently with the back of a spoon. Bake for 5 minutes more, then set aside while you prepare the filling.
4. Meanwhile, slice the potatoes very thinly and simmer them in salted water for 4 to 5 minutes until just tender but not falling apart. Drain well and leave to steam-dry for a couple of minutes. Keep the oven on.
5. Trim and wash the leeks well, then slice them. Melt the butter in a frying pan over a medium heat, add the leeks and a pinch of salt, and cook for 8 to 10 minutes until soft and sweet. Strip the thyme leaves from the sprigs and stir them through with the black pepper.
6. Spread the Dijon mustard over the warm tart base. Layer in half the potatoes, then the leeks, then the remaining potatoes, pressing gently so the layers sit snugly. Put the tart tin on a baking tray for easier handling.
7. Whisk the remaining eggs with the milk, crème fraiche and salt until smooth. Pour the custard slowly over the filling, letting it settle into the gaps. Bake for 30 to 35 minutes until the custard is set with a slight wobble in the centre and the top is lightly golden.
8. Rest the tart for 10 minutes before slicing so the custard firms up. Serve warm or at room temperature. If serving later, cool completely in the tin before unmoulding for the neatest slices.

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