Add 3 tbsps olive oil into a large skillet; heat over medium-high heat. Add onions, season with ½ tsp salt and ¼ tsp pepper. Cook stirring for 10 minutes or until the onions just begin to brown.
Reduce heat to medium, continue cooking and stirring until the onions turn golden and tender – it may take up to 15 minutes.
Reduce heat even more – to low – and go on cooking and stirring for 15 minutes more till onion slices are really soft and rich golden brown. Remove from heat, let sit for 10 minutes to cool down a little. Note: you can caramelize onions up to a day ahead of making pizza and keep them in the fridge in an airtight container.
While the onions are cooling down, place an oven rack in the middle of the oven and turn it on to preheat to 475°F/240°C/Gas Mark 9.
Place pizza dough into a shallow baking pan ( 17 by 12 inches in size). Add a tablespoon of olive oil and start pressing the dough into the pan. Be persistent – the dough will resist at first!