Place sugar in a dry, super-clean 2-quart saucepan. Heat over medium heat without stirring until sugar begins to liquefy and turn brown around perimeter of sugar—at least a ⅛inch border of melted sugar.
Stir occasionally with a wooden spoon or heatproof spatula until it turns very deep brown. It will be foaming, and smoke will start to rise. Color should be reddish-black.
Stand back as you cautiously add water: it will boil vigorously and a lot of steam will rise. Be careful.
Whisk to dissolve any seized sugar. Cool, transfer to a container to use as needed.