Place sugar in a deep heavy-based frying pan and place over low-medium heat and stir until sugar just begins to dissolve. Cook without stirring, but shaking pan occasionally, until a golden-amber caramel forms. Meanwhile, heat cream in another saucepan until almost boiling, then gradually add to caramel, taking care as mixture will spit violently. Return mixture to heat and stir until well combined and smooth. Serve sauce immediately or cool to room temperature.
Sauce will keep, refrigerated in an airtight container, for up to 1 week. Sauce will thicken once refrigerated, warm to achieve the desired consistency.