Heat the oil in a large nonreactive skillet over high heat. When the oil is hot, add the onions and sauté for 1 minute. Add the garlic, tomatoes, black and green olives, anchovy, parsley, basil, oregano, salt, and pepper. Bring to a boil, lower the heat, and simmer, stirring occasionally, for about 3 minutes.
Fold in the butter. When the butter is half melted, remove from the heat and continue to stir until thoroughly incorporated.
Yield: 1 1/3 cups