This is a traditional dish that is generally eaten with toasted baguette, although it also makes a great topping for a baked potato. To intensify the flavor, you can add either pitted black olives (about ¼ cup) or well-drained capers (2 tablespoons) to the mix.
Combine the anchovies with the parsley, garlic, and red onion in the bowl of a food processor fitted with the metal blade. Process, using quick on and off turns, to just lightly chop. Add the vinegar and process to combine.
If serving immediately, scrape the mixture into a nonstick saucepan. Place over low heat and cook, stirring occasionally, until barely warm, about 1-2 minutes. If not using immediately, scrape into a storage container, cover, and refrigerate until ready to serve. May be refrigerated for up to 1 week.
Reheat before serving with toasts or crackers.