Mustard flowers have a mild flavor that allows them to be used on all sorts of dishes. However, because they are faintly-mustard-y, they are best used on savory dishes instead of sweet ones. Try using them as a garnish for seafood, salads, egg dishes (eggs benedict, omelets, deviled eggs, quiche, etc), and more.
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