1Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8 inch baking pan.
2In a medium bowl, cream together 1/4 cup butter and 1 cup brown sugar until smooth. Beat in the egg and vanilla. Combine the flour, baking powder and salt; stir into the sugar mixture. Mix in the walnuts. Spread evenly into the prepared pan.
3Bake for 25 to 30 minutes in the preheated oven, until the brownies start to pull away from the sides of the pan. Cool completely before frosting.
4To make the frosting, combine 2 tablespoons butter, 1/4 cup brown sugar and milk in a small saucepan over medium- high heat. Bring to a boil and simmer for 2 minutes. Remove from heat, cool and beat in the confectioners' sugar. Adjust the milk or confectioners' sugar if necessary to achieve a good spreading consistency. Spread over cooled bars and let set before cutting into squares.