So, I started with a basic button-up blouse pattern that I know fits me. It's a Built by Wendy pattern that came with her Sew U book. It's actually kinda a crappy pattern in that it provides no guidance on seam allowances. You can read the gripes about that in the Amazon.com review. But it fits me well, and it's the only one I've got. Just to clarify, I'm aiming for something like this:
Buttons up the front, slight scoop neck. I had to redraw the neckline of my blouse pattern so it was lower, but I'm not going to document that here because I'm lazy and also I didn't take photos. I think you can probably figure that part out on your own though.
So, steps 1-3, go to Gertie's blog and do everything she says. Except, since this blouse buttons up the front, you can draft your collar to continue all the way around the back in one piece. In the front, it's up to you where you want the collar to end. Some collars I've seen stop an inch or so away from the center front, like in the photo below. Some meet together in the middle over the button placket, like in the photo above.
I want mine to meet together in the center, so here's what my pattern pieces ended up looking like:
You can see I drew the shoulder seam and the button placket (to the right of the dotted line) for reference. That little "I" is where a button would go. It's in the center of the placket. The center front of the collar also lines up here, because it's the middle of the shirt. The seam allowance extends beyond. I also drafted my under collar, just like Gertie directed. It's an 1/8" smaller than the upper collar along the lower edge. The neck edge is the same as the upper collar. Now, if you have enough fabric you can draft your collar pieces with just one pattern for the upper collar and one for the lower collar (and cut on the fold). If you don't have enough, you'll have to do like me and snip your pattern along that shoulder seam that I drew in. Then for each the upper and lower collar you'll have one piece that you cut on the fold and one that you cut twice. Don't forget to add a seam allowance at the shoulder seam if you do this. I forgot at first and had to recut. Also, if you aren't cutting your pieces with your fabric folded in half, make sure you flip the pattern piece between cutting two of the same - because you'll need one front collar piece that curves one way and one that curves the other way. This happens automatically when you've got your fabric folded in half, but sometimes I forget to think about that when my fabric isn't folded.
So, steps 1, 2, and 3 - follow Gertie.
Step 4 - Cut out your upper collar pieces from your fashion fabric and your under collar pieces from the fashion fabric and from your interfacing. (I used cotton batiste) Remember your seam allowances!
Step 5 - Sew on interfacing to the under collar (or iron it on if you are using fusible).
Step 6 - Join upper collar pieces to each other at shoulder seams and under collar pieces at shoulder seams.
Step 7 - Sew upper collar to under collar with right sides together, leaving the neck edge open.
This is where things get a little funky. The upper collar is a little bigger, right? So things aren't going to match up exactly. Start by pinning the ends and the center. Match the outer edges and ignore the neck edges. You'll have to to distribute the extra fabric on the upper collar evenly and use lots of pins, but it shouldn't be too difficult. They're only slightly different, after all.
Step 8 - Trim the seam allowance down to about 1/4". Clip the curves.
Step 9 - Turn the collar right side out and press, using a chopstick or some other handy tool to poke the edges out. You want to press it so that the upper collar slightly overlaps the under collar, like so:
Sorry for the blurry photo. I don't have the best camera or lighting. So in this photo the under collar is facing up, and the upper collar is just barely peeking around the edge. When you flip it over now, it will look nice and neat, like there's not even an under collar hiding around. Nice touch, right? With sewing, it really is the little things.
Soon I'll finish sewing this sucker on the shirt, and add some photos and instructions for that. If it goes well... Wish me luck!
* Drafting an under collar might not really be necessary. You could cut the under collar and upper collar from the same pattern and then just carefully trim off 1/8" from the outer edge of the under collar.