preheat oven to 350F
cream together 9 tbsp softened butter + 1 cup granulated sugar + 1 tsp vanilla
mix in 3/4 cup cacao powder
whisk in 1 egg + 1 egg yolk
add in 2/3 cup all purpose flour + 1 tbsp arrowroot powder
add batter to a lined 8×8 dish
bake for 30 min
chocolate icing: melt 1/2 cup chocolate chips + 2 tbsp butter, whisk in 3 tbsp milk of choice
spread evenly over cooled brownies and add colorful sprinkles or candies on top