Preheat oven to 350 degrees. Prepare a square 8″ baking pan by buttering it or spraying with non-stick baker’s spray. Set aside.
In medium bowl, combine flour, baking powder and salt. Stir in the sugar and sweet potato puree. Add the egg and mix to combine thoroughly. Set aside. In a small bowl or measuring cup, stir together the vanilla extract with the instant coffee until the coffee is dissolved. Set aside.
Stirring the cocoa powder into the butter
In a medium sauce pan, melt the butter over low heat. Remove the pan from heat and stir in the cocoa powder. The mixture will be thick. Stir in the vanilla mixture. Add the sweet potato batter to the cocoa mixture and stir well until the batter is uniform in color. Spoon the batter into the prepared pan and smooth the top.
Bake the brownies at 350 degrees until the top looks dry and an inserted knife comes out with just a few moist crumbs – 25 to 30 minutes.
Cool to room temperature before serving.