Preheat the oven to 350°F.
Chop tomatoes into quarters.
Simmer the tomatoes with the olive oil: Combine the chopped tomatoes and olive oil in a large saucepan. Bring to a simmer. Cook until the tomatoes are soft and the peels begin to detach from the tomato flesh.
Pass the tomatoes through a food mill: Push the warm tomatoes through a food mill, sieve or chinois to separate the tomato pulp from the seeds and skins. Stir the sea salt and citric acid into the pulp. Discard or compost the seeds and skins.