So this project has been on the back burner for a while and I'm thrilled to finally share it with you. I had trouble trouble figuring out how to make the collar lie smoothly around the neck's curve (my butterfly collar is only a half collar), but Abby at Sew Much Ado had a post today about peter pan collars that solved my dilemma - fold the shirt in half from front to back. Duh! It was definitely a V8 moment.
The basic idea is to add one layer of raw-edged knit fabric in the shape of a peter pan collar. The collar is lightweight enough that it lies smoothly without pulling the shirt. It's a great way to spruce up a lackluster t-shirt!