How to Make It
In a medium saucepan, combine the sugar with the corn syrup and water. Cook over low heat, stirring occasionally, until the sugar dissolves, about 10 minutes. Increase the heat to moderately high and simmer, brushing down the sides of the saucepan occasionally with a wet brush, until the syrup starts to turn golden. Gently swirl the pan and continue to simmer until a deep amber caramel forms, about 40 minutes total from the time you started.
Remove the saucepan from the heat. Carefully stir in the heavy cream, then stir in the butter until melted. Return the saucepan to the heat and bring the caramel just to a simmer. Remove from the heat and stir in the vanilla.
Let the caramel cool for 30 minutes, whisking occasionally. Pour the caramel into a heatproof serving bowl or fondue pot set over low heat and serve with the cake, fruit and garnishes.