Tian tart

Method

1. Steam or boil the potatoes until tender, then let them cool and cut into slices about as thick as a pound coin. While they’re cooling, warm the oil in a frying pan over a low-medium heat, then toss in the onion, bay leaf and a pinch of salt and fry until the onion is very soft and just becoming golden. This will take at least 20 minutes.
2. While the onion is cooking, prepare the tomatoes and courgettes, slicing them to about 3mm thick. Lay the tomatoes on kitchen paper and sprinkle them lightly with salt. Put the courgettes in a colander, sprinkle on some salt, turn them over with your hands and leave them to drain in the sink for about 10 minutes. Pat the courgettes dry on kitchen paper, and gently pat the tomatoes with paper too.
3. When the onion is golden, add the garlic and fry for a minute, stir in most of the thyme, then tip it all onto a plate to cool while you get on with the pastry. Don’t forget to take out the bay leaf!
4. Heat the oven to 180°C fan/gas 6 and put a heavy baking sheet in the oven to heat up. Unroll the pastry and put it on a sheet of baking paper if it isn’t already. Scatter the polenta over the pastry and spoon on the cooled onion, leaving about a 2.5cm border all around. Lay the vegetables in rows, arranging them as you like. Fold over the edges of the pastry, brush it with the crème fraîche, then grind over some black pepper and grate the cheese all over. Take the baking sheet out of the oven and carefully slide the baking paper with the tart onto the sheet.
5. Bake for 40 to 45 minutes until golden. Serve warm or cold, with the remaining thyme sprinkled on top.