A recipe for brown sugar icing paired with a sweet potato cake can be found on Epicurious.com. Another recipe for brown sugar icing paired with a chocolate cake and topped with nuts can be found at BettyCrocker.com.
The brown sugar recipe from Epicurious requires 1 cup of powdered sugar, 3/4 cup of packed dark brown sugar, 1/2 cup of whipping cream, 1/4 cup of unsalted butter, and 1/4 teaspoon of vanilla extract.
To prepare, sift the powdered sugar into a medium bowl. Stir the brown sugar, whipping cream and butter in a medium saucepan over medium-low heat until the butter has melted and the sugar has dissolved. Increase the temperature to medium-high, and bring the mixture to a boil for 3 minutes, stirring occasionally. Reduce the heat to low, stir in the vanilla, and pour the mixture over the powdered sugar. Whisk the icing for about one minute until it becomes smooth and light in color. While the icing is cooling, continue to whisk until it falls into a heavy ribbon from the spoon.
The recipe suggests spooning the icing thickly onto the cake, allowing the icing to drip down the sides. Let the icing stand for at least one hour until it is firm.