That looks similar to collars worn by men during the 18th century. I've achieved similar results with this pattern:
You could widen the collar if you wanted.
This pattern looks like it might have a better collar for your purposes, although I've never used it before:
I'd tend to stick to a pattern to ensure that the collar will sew nicely onto the neck of the shirt. The front of the shirt can be modified to achieve the look you want^^