I use sta-flo laundry starch diluted down to 50/50 with tap water. I do *ALL* of my layered twisted boutiques starched. I drench and bake each layer, then assemble. If the bow/ korker still seems floppy when assembled, I'll give it a spritz of a fast-drying aerosol starch like Niagara as a finishing spray.
I won't do twisted boutiques or layered boutiques any other way. I'm a little CDO (OCD in alphabetical order!).