1. To make the pastry, whiz the flour, butter and salt for 10 seconds until it looks like coarse crumbs. Slowly add up to 60ml of icy-cold mineral water, pulsing, until it comes together as a ball of dough. Wrap and chill for 30 minutes.

2. Heat the oven to 200C. Roll the pastry to desired thickness and use it to line a 23-centimetre-cm wide fluted tart tin. Trim the pastry, with the pastry and trim, allowing for shrinkage. Line the pastry with foil and fill with raw beans or pastry weights.

3. Bake for 10 minutes then remove the foil and weights, and bake for a further five minutes. Remove from the oven.

4. Cut the asparagus in half, and slice the bottom half, keeping the top half whole. Add the asparagus, leek, peas and zucchini to a big pot of simmering salted water. When it returns to the boil, cook for 30 seconds, then drain and refresh vegetables in icedcold water. Drain well.

5. Turn the oven down to 190C. Beat the eggs, buttermilk, nutmeg, salt and pepper together. Toss the vegetables with cheese and arrange in pastry base. Pour the egg mixture over the top, and bake for 40 minutes or until set and golden. Serve warm.