Shirt and Sweater
Cut the button up panel from the shirt, leaving an over lap on each side for sewing
Cut the sweater down the centre
Sew up the button edge so it does not flare open, leave a small bit un sewed at the bottom for some flare
Attach the button flap from the bottom of the sweater and up wards with some pins, then sew into place.
Pin the other side into place from the bottom to the top of the sweater, have a check to see if it is even with the other side, then sew into place
The striped pattern makes gives you a nice straight line to sew on
Fix up the collar how you would like it to sit, finished :)
Want to add more of the shirt to your sweater?
Use the pockets or cuffs for a more dramatic look.