Mix the flour and salt together in a large bowl. Mix the yeast with 175ml warm water and leave for 5 mins to froth just a little, then add to the flour and mix vigorously with a metal spoon. Knead the dough as soon as it comes together on a lightly floured surface for around 5 mins until smooth. Alternatively, use a mixer fitted with a dough hook, working the dough for around 5 mins on medium speed, then adding the salt towards the end of the mixing time. Leave in a lightly oiled bowl covered with a clean, damp tea towel until nearly doubled in size, about 1 hr.

Meanwhile, heat the butter in a frying pan over a medium heat and cook the leaks until softened, about 8 mins. Don’t let them colour. When soft, remove from the heat and leave to cool. Beat the eggs, crème fraîche, grated cheese, herbs and nutmeg together, and season well with plenty of pepper and some salt. Mix in the leeks.

Heat the oven to 220C/200C fan/gas 7. Line a 40 x 30cm baking tray with baking parchment. Lightly flour the work surface and roll the dough out to fit the baking sheet – it should be about 5mm thick. Make a small lip around the edge of the dough by folding the dough inward. Evenly spread the leek mixture over the dough, leaving a 1cm border. Sprinkle over the parmesan.

Cook the flamiche in the oven for around 25 mins until lightly golden on the top and the base is crisp. Remove from the oven, cut into squares and serve with salad, if you like.