double blue campanula

I think I buy a pot of these every year. Its a blue campanula with lovely double blossoms. I can't find the name on-line, but its very common plant in the supermarkets near me in the early spring. One of those bargain plants that I can't resist. I plant them outside and, as I remember, they do very well.

I had some confusion with this plant, thinking it was related to the blue balloon flowers I have in my garden in the summer. However, after some research with my Dad, I now realize that campanula and platycodon are different plants.