Step 1

To peel the tomatoes, bring a large saucepan of water to a boil. Score an X into the bottom end of each tomato. Boil the tomatoes for 1 minute and then transfer them to a bowl of ice-cold water. Peel the tomatoes and halve them. Scoop out the seeds and  roughly chop the flesh.

Step 2

Heat the oil in a large skillet over medium high heat. Sauté the onions until they start to soften, about 4 minutes.

Step 3

Stir in the tomato paste, garlic, oregano, rosemary and red pepper flakes. Cook until fragrant, about 1 minute.

Step 4

Add the tomatoes, reduce the heat to medium and simmer for 15-20 minutes until thickened.

Step 5

Use the back of a wooden spoon or potato masher to break up the tomatoes.