Centaurea montana is a perennial bachelor button. I always think the opened flowers look like the blue flame on a stovetop. They last quite a long time as a cut flower if they are cut when the blue petals are about a half inch long at the top of the bud. At this stage they kind of look like a thistle flower, but in the vase the flower will open the rest of the way and last perhaps a week.
Perennial cornflowers begin blooming in late May and continue for about a month. If they are dead-headed (or if all the flowers are cut for the house) they may continue blooming even longer. The leaves are fuzzy and silvery like lamb's ears. In good soil they may grow a couple feet tall or more, but in poor dry soil they stay more compact. They are a bit weedy, so staying compact is not a bad thing. They are easy to grow and self-seed a easily, too, so they are not for fussy people who only want rare and difficult plants.
It is quite easy to find these plants in 3" pots in the spring at places like Coleman's in Ypsilanti, but they can also be started easily enough from seed.