This placket tutorial relates to my Cornell Shirt pattern, but can be used in any other shirt pattern if you like this particular method and template.
The following photos show the sleeve placket, but if you sew View A of the shirt (which has a longer placket on the front of the shirt), the method is the same.
Cut out the sleeve plackets and interfacing pieces for the placket.
The Cornell Shirt involves separate pattern pattern pieces for the interfacing.
As this is a casual shirt, I'd recommend a lightweight iron on interfacing. You don't want anything too stiff.
Apply the interfacing to the wrong side of the fabric, following the guide on the placket pattern piece.
Mirror this for the other placket piece.
Use a fabric marker or chalk to draw the stitching line onto the fabric (follow the dashed line on the pattern piece). If you're using a pale fabric that might stain, from markers, a hand basted line of thread could do instead.
Place the right side of the placket on top of the wrong side of the sleeve (both wrong sides of the fabric will be facing up).
Match the notch of the placket to the notch of the sleeve (the notch is marked placket).
The shorter end of the placket should be on the back end of the sleeve.
Stitch around the marked lines. You may need to use a shorter stitch length around the corners for accuracy. When you reach the corner, leave the needle down in the fabric, lift the presser foot, and pivot the fabric around.
Cut through both layers of fabric, down the centre of the stitching. Stop cutting about 1cm from the top, and trim diagonally into the corners of the stitching. Get as close as you can into the corner.
Press the outside edges of the placket in towards the wrong side, using the interfacing as a guide where to fold. (Marked on the photo as 1, 2 and 3)
I like to use a the straight edge of a sheet of paper sandwiched between the fold of fabric to get a crisp edge when pressing.
Turn the placket piece through the slit so it's sitting on the right side of the sleeve.
Spread the inner placket (the shorter side) towards the slit opening.
Press the seam allowance inwards.
Take the folded edge of the inner placket and bring it over to just cover the line of stitching.
Stitch in place, close to the folded edge.Make sure the fabric at the top of the opening is neatly tucked within the inner placket once sewn up.
Take the outer placket (the taller side) and spread it out flat. Press the seam allowance in towards the centre.
Fold the outer placket over, so the folded edge covers the line of stitching.
I use the edge of a sheet of paper again for the sharp edge when pressing.
This will now be top stitched in place. But first you will need to mark where you will be sewing across the placket horizontally. If you have followed the placket template accurately, it will be 1 inch (2.54cm) down from the top edge. As you may be able to see in the photo, this line of stitching will be a little bit above the opening of the placket, but below the raw edge of the seam allowance - so everything will eventually be neatly enclosed within.
Start in the top corner, stitching down to meet the mark, and continue sewing around the top of the placket to create a square. Once you reach the corner you started at, continue stitching down - carefully following the previous line of stitching and continue going down until you reach the bottom of the placket.
I prefer to sew a cross within my square too, for added interest.
There is a detailed diagram within the Cornell Shirt instructions with a stitching order guide for both the square option or the cross option.
This is how my finished placket looks with the cross pattern top stitching.
Not that bad, hey. It may be a bit fiddly at first, so I'd recommend a few practice runs on scrap fabric until you get the hang of it.
Hope this tutorial helped.