Directions

1. Make the biga the night before. Mix the two flours, yeast and sugar in a bowl. Slowly add 150ml lukewarm water and stir to create a thick batter. Cover with a plastic carrier bag or dry tea towel and leave in a warm place overnight to ferment.
2. The next day, add the other flours, yeast, olive oil and 1 tsp salt to the biga, then gradually mix in enough water to make a soft, wet dough that still holds its shape (we used 200- 220ml). Cover and leave to rise for 2-4 hrs or until tripled in size.
3. Once the dough has risen, punch the dough to knock the air out, then tip out onto a heavily floured surface. Knead in the flour until the dough stops sticking to your hands - it should be very soft and springy, but not so wet that it sticks to the surface. Divide the dough into two balls. Roll one out to make a large pizza base approx 1cm thick (or divide in half again to make two smaller pizzas). The other ball should be frozen for use at a later date. Heat oven to 210C/ 190C fan/gas 61/2 . Transfer the base to an oiled baking sheet and prove for 5 mins while you prepare the toppings.
4. Using a mandolin or sharp knife, slice the potatoes very thinly. Pat away any excess moisture with a clean tea towel. In a bowl, toss the potato slices and thyme leaves in the olive oil and season. In another bowl, mix the garlic and creme fraiche, then spread onto the pizza base with the back of a spoon. Lay the potato slices on top and drizzle with any remaining olive oil or thyme from the bowl. Bake for 15-20 mins until the base is puffed and golden and the potatoes are crisping up around the edges.
5. Meanwhile, make the pistou by blitzing all the ingredients in a food processor. To serve, drizzle the pistou over the pizza and scatter over some mint leaves.