Step 1

Pulse both the flours, the thyme leaves and butter together in a food processor until the mixture resembles fine breadcrumbs. Pour in 4 tbsp cold water and pulse again until a dough forms. Add another ½ tbsp water at a time until it comes together into a ball. Chill for at least 30 mins. This can be made up to two days ahead and chilled.

Step 2

Meanwhile, heat half of the oil in a large frying pan over a low heat and fry the leeks with a large pinch of salt for 10-15 mins until softened. Add the garlic and cook for a couple more minutes until fragrant, then pour in the wine. Turn the heat up and continue to cook until the wine has completely evaporated, about 5 mins. Remove from the heat and stir in the miso. Season lightly, then tip out onto a plate and spread out to cool slightly.

Step 3

Roll the pastry out between two sheets of baking parchment into a rough 30cm circle. Remove the top sheet of parchment and spread over the leek mixture, leaving a 4cm border. Slide the leek-topped pastry, still on the baking parchment, onto a large baking tray. Keep chilled until you’re ready to bake. Will keep chilled for a day.

Step 4

Heat the oven to 200C/180C fan/gas 6 and put a second large baking sheet in the oven to heat up. Heat the remaining oil in a large frying pan over a high heat and fry the mushrooms with some seasoning for 10 mins until browned all over. Scatter the mushrooms over the leek mixture in an even layer. Fold the edges of the pastry over so it’s just overlapping the filling mixture (this doesn’t have to be neat). Brush the pastry with the beaten egg, then sprinkle over the cheese and carefully slide the galette on its baking parchment onto the hot baking sheet. Bake for 30-35 mins until golden and crisp.