How do you say yummy cookie in french?

There isn't a single perfect translation for "yummy cookie" in French, but here are some options:

Informal:

* Un cookie délicieux (a delicious cookie)

* Un cookie succulent (a succulent cookie)

* Un cookie trop bon (a really good cookie)

* Un cookie miam miam (a yummy yummy cookie - using the onomatopoeia "miam miam")

More formal:

* Un cookie exquis (an exquisite cookie)

* Un cookie savoureux (a flavorful cookie)

The best option really depends on the context and the level of formality you want to convey.