A flask has a body, base, mouth, and one or more indicia to enable preparation of beverages with a desired temperature. Specific embodiments include the preparation of baby formula and tea. The one or more indicia can show one or more levels, quantities, or both. A level or quantity contained within the flask has a proper percentage of liquid, as calculated and so embedded as a feature into the flask, while the corresponding indicium on the flask for the level or quantity shows the total amount of liquid needed, so that the preparation of temperature sensitive beverage with a desired temperature will be convenient and quick. In another aspect, a method for preparing a temperature sensitive beverage fills a flask up to a volume shown by one or more indicia, heats the liquid in the flask, and combines the heated liquid with unheated liquid to attain a beverage with a desired final volume and a desired final temperature.
