For the Dough:
Crumble the fresh yeast or sprinkle the dried yeast and a pinch of sugar into 3 tablespoons of lukewarm water. Be sure that the water is lukewarm (110 - 115 F. - neither too hot nor too cold to the touch). Let it stand for 2 to 3 minutes, then stir the yeast and sugar into the water until completely dissolved. Put the cup in a warm, draught-free place for 3 to 5 minutes, until the yeast bubbles up and the mixture almost doubles in volume. If the yeast does not bubble, start over again with fresh yeast.
Sift the flour and salt into a large, warmed bowl. Make a well in the centre of the flour and pour in the yeast mixture, 3/8 pint of lukewarm water and 3 tablespoons of the olive oil. Mix the dough with a fork or your fingers.
When you can gather it into a rough ball, place the dough on a floured board and knead it for about 15 minutes, until smooth, shiny and elastic. Dust the dough lightly with flour, put in a large clean bowl and cover. Place the bowl in a warm, drought-free spot for about 1 1/2 hours, until the dough has doubled in bulk.
Now preheat the oven to 450 F. Punch the dough down with your fists and break off about one quarter of it to make the first of the 4 pizzas. Knead the small piece on a floured board or a table for a minute or so, working in a little flour if the dough seems sticky. Flatten the ball into a circle about 1 inch thick with the palm of your hand. Hold the circle in your hands and stretch the dough by turning the circle and pulling your hands apart gently at the same time.
When the circle is about 7 or 8 inches across, spread it out on the floured board again and pat it smooth, pressing together any tears in the dough. Then roll the dough with a rolling pin, from the centre to the far edge, turning it clockwise after each roll, until you have a circle of pastry about 10 inches across and about 1/8 inch thick.
Crimp or flute the edge of the circle with your thumbs until it forms a little rim. Dust a large baking sheet lightly with corn meal and gently place the pizza dough on top of it.
Knead, stretch and roll the rest of the dough into 3 more pizzas.
FOR THE TOPPINGS
Pour 6 tablespoons of the tomato sauce on each pizza and spread it with a pastry brush or the back of a spoon.
To make a cheese pizza, sprinkle the sauce with 6 tablespoons of mozzarella and 2 tablespoons of grated Parmesan. Dribble 2 tablespoons of olive oil over the pizza and bake it on the lowest shelf or the floor of the oven. Reduce the oven temperature to 400 F after 5 minutes and cook for about 10 minutes in all, until the crust is lightly browned and the filling bubbling hot.