In a large bowl, combine the yeast and sugar with 330ml warm water and stir to blend. Let the mixture stand for about 5 minutes until foamy. Stir in the oil and salt.
Slowly add both flours, a little at a time, stirring until the dough forms a ball. Knead on a floured work surface until elastic. If necessary, add extra flour to stop the dough from sticking.
Place the dough in a large bowl, lightly greased with a little olive oil. Cover with clingfilm and set aside to rise in a warm place until doubled in size (around 1-2 hours).
Meanwhile, prepare the tomato sauce. Put the tomatoes and juice in a pan and simmer until reduced to a thick sauce. Set aside.
When the dough has doubled in size, punch it down and divide in two. If making both pizzas immediately, put half of the dough aside and cover with a damp tea towel. To one just pizza now, wrap the remaining half of the dough in clingfilm and chill in the fridge (use the dough the next day).
Preheat the oven to 220°C, fan 200°C, gas 7. Stretch out the dough (or use a rolling pin to roll) and place on a baking tray. Spread the tomato sauce over the top. Sprinkle with the marjoram and top with the mozzarella slices. Bake for about 10 minutes, until the crust is golden and the cheese has melted.