from Good Eats 'n Sweet Treats who got it from Culinary Concoctions by Peabody who got it from Baking: From My Home to Yours
2 cups sugar
1/2 cup water
1-1/2 tbsp light corn syrup
2/3 cup heavy cream
2 tbsp unsalted butter, at room temperature
Put the sugar, water and corn syrup in a medium heavy bottomed saucepan, stir just to combine the ingredients and then put the pan over medium-high heat. Heat, without stirring , until the caramel turns deep amber., 5-10 minutes. Lower the heat a bit and, standing back from the saucepan add the cream and butter. When the spatters are less vehement, stir to calm down the caramel and dissolve any lumps. Let cool slightly before serving.