Preheat oven to 350 degrees and grease a 8 in. square baking pan.
Combine brown sugar, flour, walnuts, baking powder and salt into a large mixing bowl.
Add in butter, egg, and vanilla and beat with a hand mixer until smooth.
Pour batter into baking pan and bake for 20 to 30 minutes until baked through and golden.
In a small saucepan bring butter, brown sugar and milk too a boil.
Stir lightly and then reduce heat. Leave on heat for about one minute, and then remove from heat.
Let cool COMPLETELY, and add in confectioners' sugar, the more you add the thicker it will get.
Stir well with a spoon until smooth.
Icing your brownies.
Serve and enjoy!