Heat oil and butter in a large pot. 

Add onion, garlic and tomato paste and cook over low heat, stirring occasionally until onions are soft.

While onions are cooking, blanch tomatoes in boiling water, then peel.

Once onions are soft add all other ingredients and simmer slowly in semi-covered pot for 45 mins.

Stir occasionally to prevent sticking.

Remove lid and cook further 10-15 mins until sauce is quite thick.