Watercress

During cooking it loses its tangy, bittersweet flavor and becomes mild.

An excerpt from the article 20 facts about watercress

It forms a good combo with cream and butter, which makes it possible to use it to make sauces for fish, pâtés, vegetarian tarts, white meat dishes, and cream soups. The French add it to anchovies, so they no longer use salt or pepper.