01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Whisk melted butter and sugar in a large bowl until combined. Add eggs and vanilla; whisk until smooth.
03 - Sift cocoa powder, flour, salt, and baking powder into the bowl. Fold gently with spatula until just combined.
04 - Pour batter into prepared pan, smooth top. Bake 28-32 minutes until toothpick inserted comes out with moist crumbs.
05 - Let brownies cool completely in pan on wire rack before frosting.
06 - Beat softened butter with powdered sugar until light and fluffy. Add milk, vanilla, and food coloring; beat until smooth.
07 - Spread frosting evenly over cooled brownies. Cut into squares and serve.