If You Can't Beat Them, Eat Them! Volume 3

Like most other species of wild mustard, blue mustard is edible. While some people may be put off by the stale smell of the plant, its leaves are eaten nonetheless. Young leaves may be used in salads containing other wild or dark leafy greens, such as dandelion. Larger, more mature leaves can be cooked, much like turnip greens or collard greens.

The most common recipes for mustard greens come from the Southern states in the US and involve cooking with pork and serving with vinegar. I found this excerpt in the comments section of a wild mustard article on Eat the Weeds:
"Don’t pick the big leaves at the bottom of the plant. They will be sandy and more likely to be bitter. Don’t make extra work for yourself by picking sandy greens. Simmer them in a covered pot for about an hour (until tender) in about 3/4 – 1 inch of seasoned water (salt, pepper, and if you like it, add bacon fat), stirring occasionally, and checking the water. When they are nearly done, remove the cover to reduce the liquid, which is known as “pot likker” or “pot liquor.” Pot likker is nutritious and it is used for sopping cornbread or making soup." 
Although these instructions are not specific to blue mustard, I think that it would work out just fine.



Where I live, blue mustard grows in any available open space: along the roadside, in vacant lots, it will even make its way into your lawn if you let it!