For the white dough, pop the water into a mixing bowl fitted with the dough hook attachment and add the ferment, fresh yeast, flour and salt and mix on low speed for 4-5 minutes.
Once everything is well incorporated, turn the mixer up a speed and continue to mix for a further 5 minutes or until smooth and elastic.
Transfer the dough to a bowl and cover with a clean cloth. Leave to rest for at least 20 minutes.
For the Flamiche, pop the butter and oil into a pan and sweat the sliced onions for a few minutes until starting to brown. Add the leeks and continue to cook until the leeks are softened.
In a separate bowl mix together the creme fraiche, egg, nutmeg and season well before adding the leek and onion mix to the bowl. Set to one side.
Turn the rested dough onto a lightly floured surface and split in half. Open one half of the dough into a pizza type circle before topping with half the mixture and grating over half the cheese.
Transfer the Flamiche to a floured peel before sliding it into your wood fired oven. The oven should have a small bed of embers with no active flame and be running around 220 degrees.
Bake for around 6 minutes and serve!
To make the white sourdough starter;
Stage 1 – Mix all the ingredients together in a large plastic container, cover with a freezer bag large enough to cover the entire container, and leave in a warm place for 24-36 hours without disturbing it. The mixture will start to smell a little lactic, darken in colour and bubbles will begin to form- these are signs that fermentation is underway and you are ready for stage 2.
Stage 2 – Add the flour and water to your ferment, mix well, cover as before and leave in a warm place for a further 24-36 hours. At the end of this stage the mixture will have expanded a little and be starting to smell sweet and lightly fermented. That means you’re ready for stage 3.
Stage 3 – Add the flour and water to your ferment, mix well, cover as before and leave in a warm place for a further 24-36 hours. By the end of this stage, you should have a total of 800g of ferment. Use 300g to make the Flamiche and keep the rest in the fridge to make another batch of bread.