Make the biga the night before. In a bowl, combine the two flours, yeast and sugar. Slowly add 150ml lukewarm water, stirring to create a thick batter-like dough. Cover with a plastic carrier bag or dry tea towel and leave in a warm place overnight
For the second stage, add the flours, yeast and olive oil along with 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 around 200ml-220ml water). Cover and leave to rise for 2-4 hours or until tripled in size, being careful that it doesn’t over prove and collapse on itself
Once the dough has risen, knock it back in the bowl 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 into 2 balls (freeze one to use later) use the other to make either 2 small or one large pizza rolled out with a floured rolling pin to approx. 1 cm thick. Heat the oven to 210C/190C fan/gas mark 6 1/2. Transfer the base to an oiled baking sheet. Prove this for a further five minutes while you get the topping ready
Beat the crème fraiche, garlic and gorgonzola together to make the base. Spread it across the pizza dough. Toss the kale and red onion in a bowl with olive oil, salt and pepper. Add this to the top of the pizza base along with the blackberries, extra gorgonzola and walnuts, drizzle with olive oil and season with thyme. Bake for 10-15 mins, until the base is puffed and golden.