In a small saucepan, heat the butter over medium heat until solids separate and begin to brown. Remove from heat. In another saucepan, heat sugar over medium high heat. As sugar begins to melt, swirl the pan frequently. Continue to cook and swirl until the sugar begins to smoke slightly and turns a deep brown color. Remove from heat then pour in the butter. Pour in the heavy cream and whisk to mix well. Set aside to cool to room temperature before glazing cake.