I've tried both ways. Here's my take on it.
For several years I diluted the cornstarch with a bit of cold water then
added boiling water. That worked but it would separate so you have
to keep stirring. I put the starched fabric in ziploc bags and keep
it in the fridge for 24 hours.
Then I tried to cook the starch. The good thing with cooking the starch
is that it does not separate. The bad thing is is that it made a mess
on my iron even on dry fabric. It was a nightmare. Maybe I cooked
the starch too long? But anyway, after this experiment I'm back to
starching the old way.
You could try both ways and see which method you like.
