To make dough: In a small bowl, dissolve sugar in 250ml warm water; in a separate small bowl combine the yeast, 60g flour and 125ml warm water. Mix together and let rest in bowl for about 20 minutes, until foamy.
Meanwhile, in a medium bowl mix together remaining flour with polenta and salt; remove half of this mixture from bowl and stir the sugar-water mixture into bowl. When well mixed, return second half of flour/polenta mixture to bowl and mix all together; then stir in yeast mixture. Knead dough on a lightly floured surface until smooth and elastic, about 8 to 12 minutes. Place dough in a lightly oiled bowl and cover with cling film. Let rise until doubled in volume.
Preheat oven to 230 C / Gas 8.
To make stuffing: In a large bowl combine the sausage, mozzarella cheese, Parmesan cheese, pepperoni, onion, pepper, oregano and garlic. Mix well.
Press half of the dough in the bottom and up the sides of a lightly greased deep baking tin. Bake base in preheated oven for 4 minutes, then add the stuffing mixture to the base and cover with top crust; seal edges together with fingers, and trim excess. Slit top crust to allow steam to vent during baking; top with passata.
Bake on lower rack at 230 C / Gas 8 for 45 minutes, or until crust is golden brown. Remove from oven and allow to cool for 5 minutes, then cut and serve.