In a medium, heavy-based saucepan, melt the butter. Stir in the two sugars, the salt, water, and corn syrup. Bring the mixture to a boil over medium-high heat, stirring to dissolve the sugars. Let the mixture boil for 5 min., stirring often. You'll see big, slow bubbles as it boils. Remove the sauce from the heat. Carefully whisk in the cream and vanilla (the sauce may sputter). Allow the sauce to cool to warm before serving.