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2 Add the onion and saute until soft, about 5 minutes. Add the garlic and cook 1 minute longer. 3 Add the tomato paste and then the tomatoes, cook for 2 - 3 minutes, and then pour in the chicken stock. 4 Simmer briskly until the sauce is thick, 20 - 30 minutes. For a finer consistency, pass the sauce though a wire-mesh sieve into a clean saucepan. 5 Stack the basil leaves, roll them up lengthwise, and cut across the roll very thinly to make a chiffonade. 6 Stir in the basil. Whisk in the butter