Put 175g butter, wholemeal flour, half the thyme and a pinch of salt in a food processor and pulse until it starts to clump together. Add 2-3 tbsp cold water and pulse again until it forms a ball. Wrap and chill for 20 mins.

Meanwhile, heat the remaining 2 tbsp butter in a frying pan, and fry the mushrooms and onions for 10 mins until soft and lightly golden. Season well and remove from the heat.

Heat the oven to 220C/fan 200C/gas 7. Add a large flat baking sheet to the oven to heat up. Whisk the soft cheese with half the chives, remaining thyme and all the garlic. Season well.

Roll the pastry out in between two sheets of parchment to a rough rectangle shape, the thickness of a £1 coin, about 30x40cm. Remove the top layer of parchment and smooth over the soft cheese mixture, leaving a 5cm border. Spoon over the mushrooms, in an even layer over the soft cheese, then fold over the 4 sides of the border to overlap the filling slightly. Trim the sides before you fold over if you need to, but will look lovely when baked either way. Glaze the pastry with egg.

Using the parchment to help you, slide the tart onto the hot tray with the paper. Bake for 35-40 mins until the pasty is cooked though, and crisp. Scatter with the remaining chives to serve, along with a green salad.