forestofglory

I also longed for a variable-temp teapot until I discovered how to systematically and quickly cool down water right off the boil: pour the water between two vessels a set number of times.

If you're boiling in an open container (or a glass kettle), there's the traditional rubric for determining temperature by the shape and frequency of the bubbles:

Shrimp Eyes, Crab Eyes, Fish Eyes, Rope of Pearls, Raging Torrent