For the caramel icing:
- 1 cup dark brown sugar, firmly packed
- 5 tablespoons unsalted butter, cut into a few chunks
- Generous 1/4 teaspoon salt
- 1/4 cup milk
- 1/2 teaspoon pure vanilla extract
- 1 cup confectioners’ sugar
When the cupcakes have cooled, make the icing. Put the dark brown sugar, butter and salt in a medium saucepan, and melt them together over medium heat, stirring often.
Bring the mixture to a boil and add the milk and vanilla. Boil for 3 minutes, stirring occasionally. Dump in the confectioners’ sugar all at once and beat with a wooden spoon until the icing is thickened and smooth.
Quickly ice the cupcakes by holding each by the base and dipping the tops in the hot icing, rolling them slightly to coat evenly.
Turn them quickly upright so the icing will even out while it’s still warm and will set smoothly.