Sharon Schamber shows what is, IMHO, the most efficient way to make HSTs into squares - which is how we usually use them. She demos her method here:
www.youtube.com/watch?v=fFu1_4ksHj8
She cuts the squares AFTER the HSTs are sewn together, thus no stretching while ironing, and no need to square up. I'll repeat that - YOU ONLY CUT EACH SQUARE ONCE. NO SQUARING UP :!: :!:
Fons and Porter use a variation of Sharon's method - sew 2 bias strips together, and then cut squares from the strips.
With Sharon's method, you can cut enough squares for an entire quilt. It's the SAME method. It just depends on HOW MANY finished squares made from HSTs you need.
No paper foundations to tear off, no stretchy bias to get out of shape. Just oodles of finished squares made of HSTs. The main thing is, you have to be careful when you iron the strips together at the beginning! But you've starched the fabric heavily, so it's not going to stretch!!!
Best of all, YOU DON'T HAVE TO BUY A SPECIAL NEW RULER :D - and you probably already use the spray startch in your quilting cave. The wonder tape that Klue mentioned would work for marking lines for cutting if you're at all timid about using your rotary cutter after going to all the trouble of sewing all those bias strips together :!: