Pile the flours and sea salt onto a clean surface and make a well in the centre. Add the yeast and sugar to 650ml lukewarm water, mix together and leave for a few minutes, then pour into the well. Using a fork and a circular movement, slowly bring in the flour from the inner edge of the well and mix into the water.
Continue to mix, bringing in all the flour – when the dough comes together and becomes too hard to mix with your fork, flour your hands and begin to pat it into a ball. Knead the dough by rolling it backwards and forwards, using your hands to stretch, pull and push the dough. Keep kneading for 10 minutes, or until you have a smooth, springy, soft dough.
Place the dough in a lightly greased bowl, cover with clingfilm and leave in a warm place to to prove for 45 minutes, or until doubled in size. To assemble the pizzas, divide the dough into equal balls (You can wrap some dough in clingfilm and freeze for another day if you don't want to use the whole batch). Flour each dough ball, then cover with clingfilm, and leave to rest for about 15 minutes – this will make them easier to roll it thinly.
Dust a clean surface and the ball of dough with a little flour or semolina, and roll it out into a rough circle, about ½cm thick. Tear off an appropriately sized piece of tin foil, rub it with olive oil, dust well with flour or semolina and place the pizza base on top. Continue doing the same with the remaining dough, dust with a little flour so you can pile them up. Cover with clingfilm and place in the fridge. When you're ready to cook them, preheat the oven to 250°C/500°F/gas 9.
At this stage you can apply your toppings. If you can, cook the pizzas on a pizza stone in your conventional oven – if not, cook them one by one on pieces of tin foil directly on the bars of the oven shelf, towards the bottom of the oven (If you're going to cook your pizzas on the bars of the oven, make sure they're not too big – otherwise they'll be difficult to manoeuvre). Cook for 7 to 10 minutes, until the pizzas are golden and crispy.