The best method (arguably not very energy efficient) is a Zojirushi water boiler that keeps the water hot (175F, 190F, 200F) and boils when a temperature change is detected.
It’s so nice to have if you drink a lot of tea, or as some Asian households prefer, hot vs room temp water.
How many British Thermal Units does it require to heat one gill of water to 212F from a room temperature of 72F if you have a 1/2 horsepower electric kettle?