Step 1

For the pastry, whiz flour, butter and a pinch of salt in a food processor for about 10 seconds until it forms coarse crumbs. Gradually pour in mineral water, pulsing for 1-2 minutes, until it forms a ball. Enclose in plastic wrap and chill for 1 hour.

Step 2

Cook kumara in boiling salted water for 15 minutes or until tender. Drain and cool.

Step 3

Preheat oven to 180C. Place pastry on a floured surface. Cover with plastic wrap to prevent sticking. Roll out to about 5mm thick and use to line a 20cm loose-bottomed tart pan. Trim excess. Prick base with a fork, line with baking paper, then fill with uncooked rice or pastry weights. Bake for 10 minutes. Remove paper and weights, then bake for 5 minutes or until golden and dry.

Step 4

Increase oven to 190C.

Step 5

Beat eggs, cream and milk with a whisk until just combined. Stir in cheese and nutmeg, then season. Arrange pancetta and kumara in pastry case, then scatter with rocket. Pour in filling and bake for 30-40 minutes until set. Serve warm.