Because onion flowers are so strong, it may be better to use individual blossoms in smaller amounts than a whole head to keep their flavor from being too intense. They can be used to garnish all sorts of savory dishes.
Some edible flowers may wilt or change color when exposed to vinegar, so if using a vinegar-based dressing on salads containing edible flowers, test it on a few blossoms ahead of time and/or add it at the last second.
Edible Flower Recipes