This sauce can be made ahead and refrigerated. Serve at room temperature or reheat in microwave. Prep: 5 minutes, Cook: 25 minutes.
Pour heavy cream into a small saucepan over low heat. Scrape seeds from vanilla bean into cream, and bring to a simmer. Remove from heat; let steep 20 minutes. (If using vanilla extract, omit the steeping process, and just add to the cream.)
Combine sugar and water in a small heavy saucepan over medium-high heat; cook until sugar dissolves, wiping down sides of pan with a pastry brush dipped in water to prevent sugar crystals from forming. Boil sugar mixture 5 minutes or until amber colored. Remove from heat, and carefully add warm vanilla cream, stirring until combined. Add butter; stir 1 minute or until butter is melted. Serve warm.