Tutorial for Peter Pan collarYou can make this collar for any blouse or shirt as long as it has an opening in the front.
Pattern drafting1. Take the center front piece and center back piece of your pattern. If it has darts at the shoulder temporarily move it/them to the side (a).

2. Lay the pattern pieces shoulder to shoulder, overlapping 1-2 cm at the armhole (b).
3. Take a piece of paper and put it over the pattern. Trace the neckhole, but lower it 0,5 cm at the front (c )
Draw a line 6,5 cm from the neckhole and draw the center back and center front lie as the picture shows.

4. Cut out the collar pattern and make two folds, 1cm at the outer line and 0 at the inner (d). Make sure that the pattern still is flat.
5. Shape the front of the collar (e).
Sewing the collar6. Fold the fabric and put the pattern with the side marked center back against the fold. Cut it out with 1 cm seam allowance. Do the same thing again, so that you have two pieces.
7. Put fusible interfacing on one of the pieces. Put the pieces right sides together and sew 1 cm in along the outer side (marked in pink).

8. Press the seam apart cut little triangles in the seam allowance at the rounded part, and turn it so that the right sides are out. Press the collar so that the seam isn't visible from top. Sew about 2-5 mm in all around the outer edge (pink). This will help the collar keep its shape.
9. Attach the collar to your garment.
I'm not very good at explaining things, but I hope you understand it. Good luck!