Preheat the oven to 200 degrees C/ 392 F, I use a fan assisted electric oven please adjust according to your own oven.
Add the flour to a large bowl. Add the salt to one side of the flour then add the yeast to the other side. Make a well in the middle and pour in the warm water and olive oil. Mix with a spoon until you have a wet dough.
Turn the dough out into a floured surface and knead for 5 minutes, add a little olive oil to the bowl then place the dough back in the bowl. Cover with cling film and a tea towel then leave in a warm place for the dough to rise. In warm weather, this should only take about 30 minutes.
Then turn out the dough onto a floured surface and knead again for a couple of minutes.Divide the dough in half, using your knuckles make an edge in the dough then pull the dough out to make two good size rounds.
To make the pizza sauce
Heat the olive oil in a medium saucepan. Add the onion and cook until soft, about 10 minutes. Add the garlic, oregano and then the tomatoes, tomato puree and balsamic vinegar. Bring to the boil then reduce to a slow simmer, stirring occasionally, cook until the sauce has reduced by about a third.Once the sauce is thick and reduced, you can serve it as is or use a hand-held blender to blend the sauce for a smooth pizza sauce.
Assemble the pizzas
Sprinkle the polenta over two baking trays.Add the pizza bases to the trays, cover the bases with the pizza sauce.Divide the mozzarella between the pizzas. I tear the mozzarella but you can grate it if you wish.Add the onions to the mozzarella, next add the spinach and the tomatoes. Finally, crumble the feta over the pizzas. Drizzle a little olive oil over the pizzas then bake in the oven for 15 minutes.Once cooked, add the pine nuts and black pepper. Serve immediately.
This recipe makes two pizzas. Please see post for tips on freezing dough or sauce if you only want to make one pizza.
You can cut down on the time by buying your pizza dough or base.
If you want to make a gluten-free version on this you could use your favourite gluten-free base.