This question may sound silly, but humor me. I've been using growlers to make starters since, well, forever. I boil in a pot, chill said pot, then pour and pitch my yeast.
I recently bought a 5L borosillicate flask needing more headroom for bigger starters. I know many folks boil directly in the flask, and then plunge the flask in an ice bath to chill it to pitching temps.
How do you measure the wort temperature while chilling large flasks?
I use a thermapen, and the probe won't come close to reaching the wort level in the 5L flask, even with a big starter.