Rinse the tomatoes. Cut the tomatoes into about 10 thin slices with a sharp knife. You can also try with the mandolin but if your tomatoes are very ripe it is easier to cut with a knife.Place them side by side on a platter.
Cut the red onion into very fine pieces and sprinkle it over the tomato.
Place an anchovy on each tomato.Sprinkle the tomato with a little salt. (note, not too much because anchovies are already salty) Drizzle with the olive oil... and that's all...Are you a fan of capers? Then you can sprinkle some on top...
"Coeur de boeuf" tomatoes are fantastic in this dish. The sweeter the tomatoes, the better...they taste strong with the saltiness of the anchovies. This dish is on many menus here in the south, simple but super tasty!