I found a nice cotton shirt in a charity shop in Creiff. It was XL, which gave me quite a lot of fabric.
The blouse is based on a dress from a norwegian sewing magazine, Symagasinet, but I had to change it quite a lot to make it work with the shirt. The shirt had princess seams on the front, so I left out the darts from the original pattern. I also made the blouse back in one piece, keeping as much of the yoke as possible, and added 2 darts.
I was worried that the binding at the neck opening might stretch, so I sewed a piece of tape in to reinforce it. The hem is curved, similar to the original shirt. If I'd had enough fabric, I would have made the sleeves longer, but this is a nice summer blouse.