Bring a saucepan of water to a boil. Cut a shallow X in the bottom of each tomato, blanch for 30 to 60 seconds, and transfer the tomatoes immediately to ice water.

Slip the skins from the cooled tomatoes, remove the cores, and chop the tomato flesh into bite-size pieces. Reserve all the juices because they help create the cooking liquid.

Melt the butter in a saucepan or Dutch oven over medium heat. Add the onion, celery, and green bell pepper, then cook for about 5 minutes until the vegetables are slightly softened.

Add the chopped tomatoes, sugar, salt, and black pepper to the pot. Stir gently so the seasonings are distributed without breaking down the tomatoes too quickly.

Bring the mixture to a gentle simmer and cook uncovered for 20 to 25 minutes. Stir occasionally until the vegetables are tender and the tomato juices have thickened slightly; add up to 2 tablespoons of water only if the tomatoes are not releasing enough liquid.

Taste the stewed tomatoes before serving and adjust the salt, pepper, or sugar as needed. Serve hot as a side dish, spooned over bread, rice, potatoes, or your favorite savory main course.