And here’s the follow-up from the Smocked skirt – prep post. Thanks to Prudent Baby’s explanations on how to smock: http://prudentbaby.com/2010/03/baby-kid/sweet-shirred-summer-dress-pattern-2/
If any are interested in making it: cut a piece of fabric roughly 150 cm wide by 55 cm high. Stitch sides together to form a wide tunnel. (Zig-zag seam or French Seam). Hem top and bottom. Shir/smock the top 13 cm, I made a line roughly every 1 cm. The trickiest part is getting the smocked lines not too tight, not too loose.
Or same info on Burdastyle: here