In a medium saucepan with high sides, combine the sugar and corn syrup with 1/2 cup water.
Stir the mixture gently so you don't slosh any of it up the sides of the pan.
Turn the heat to medium-high and continue stirring until the sugar dissolves. Increase heat to high, stop stirring and allow mixture to boil.
Once it begins to turn a rich caramel color (if you don't want to eyeball it, take the caramel to 300 on a candy thermometer), remove it from the heat, add the butter and cream and stir until combined.
You can save the caramel sauce, tightly covered, in the refrigerator for up to 1 week. Let it cool to room temperature before using it on cakes, ice creams or quick breads.
If you want a warm topping, heat the caramel sauce in short bursts in the microwave or in the top of a double boiler.