Mash potatoes & add other wet ingredients. Stir well.
Add all dry ingredients except chocolate chips. Stir to combine. Add chips.
Pour batter into an 8x8 pan and bake at 350° for 25-30 minutes.
Allow to cool and top with icing if desired. Cut into 9 brownies.
Icing: Add all ingredients to a large bowl. Whisk or use a hand mixer to blend for 2-4 minutes into smooth and fluffy. Top the cooled brownies and add crushed candy canes or sprinkles if desired.