In a small saucepan, bring the sugar, water and lemon juice to a boil. Brush down sides of pan with a pastry brush dipped in water. Add the corn syrup and cook until golden. Remove from heat and stir in the heavy cream in a slow but steady stream. If the sauce is lumpy, return the pan to the heat and stir until smooth. With pan off the heat, stir in the butter.
Serve over ice cream and nuts (like walnuts or pecans).