Meanwhile, heat a large frying pan over medium heat. Add the olive oil and heat for 1 minute. Add the onion and cook stirring for 2–4 minutes. Add the garlic and anchovies and cook, stirring for 3 minutes. Add the tomato paste, diced tomatoes, crushed tomatoes and oregano and gently simmer for about 8–10 minutes. Add the red chilli flakes (if using), capers and pitted olives, and stir through the sauce.
3 tbsp extra virgin olive oil, 1 brown onion, 3 cloves garlic, 3 anchovy fillets, 1 tbsp tomato paste, 2 roma tomatoes, 400 g canned crushed tomatoes, 1 tbsp oregano, 1 tsp red chilli flakes, 2 tbsp capers