Crush garlic with your palm and remove peel. Add olive oil to a saucepan and heat over medium. Add anchovies and let cook, breaking up with a spoon.
Once the anchovies are broken up and mostly dissolved in the olive oil, add the garlic clove, canned tomatoes, and a hearty pinch of salt. Mix to combine and let simmer on low heat, stirring occasionally, for 15 min. (If the sauce is splattering a lot, partially cover to avoid the mess.) Season to taste with more salt and pepper before serving. (For a smoother sauce, purée or blend before using.)