Add 1/3 cup water to a medium saucepan and set over high heat. Carefully pour the sugar directly into the center so none of it splashes up the sides of the pot. Bring to a boil and cook until the sugar starts to turn brown. Do not stir the pot. If you need to, gently swirl the pot to help melt all the sugar. Once the sugar turns a deep brown color, remove from the heat and carefully pour in the cream, taking care as it will splutter a little. Add the butter, salt and vanilla. Swirl the pot until the butter dissolves completely and evenly into the caramel sauce.
Drizzle a little of the caramel sauce into 2 tall milkshake glasses. Add the ice cream, milk and the remaining caramel sauce to a blender. Blend until smooth and pour into the glasses.
Cook's Note: For an adult version of this drink add 1 1/2 ounces rum to each milkshake!