In a large, heavy-bottomed saucepan, combine sugar and water. Stir to moisten the sugar and heat over medium-high without stirring until the syrup starts to color. If needed, use a damp pastry brush to wash down the sides of the pot.
Monitor the syrup closely; when it reaches a medium amber color, be attentive as the color will deepen rapidly. Within the next minute, the caramel will transform into a rich mahogany brown, with bubbles turning tan and the possibility of wisps of smoke. Immediately remove from heat, swirling the pot to dissipate heat.
Place the pot on a cool burner and slowly pour in the cream. Expect vigorous bubbling, and allow it to subside before whisking until smooth. If the cream is too cool, it may cause the caramel to seize. In such cases, gently heat the pot over low heat and stir until the sauce liquefies.
Cool the caramel sauce to room temperature. Store it in an airtight container in the refrigerator for up to 1 month.
Before use, reheat the sauce in a double boiler or microwave. This versatile dark caramel sauce is perfect for enhancing the flavor of ice cream, cake, serving as a warm dip for tart apple slices, or simply enjoying off a spoon.