Preheat oven to 350 degrees F. Lightly grease a 9x9-inch baking pan or line with parchment paper.
Place the 1 cup of butter and chocolate chips in a large microwave safe bowl. Microwave on high in 30 second intervals, stirring after each, until melted and smooth. Set aside to cool completely.
In a large bowl mix together eggs and granulated sugar with a whisk or an electric mixer on medium speed until well combined. Beat in vanilla extract.
Beat cooled chocolate and butter mixture into the eggs and sugar until combined. Beat in baking powder, salt, and flour until just combined. Pour brownie batter into prepared baking pan.
Bake brownies for about 30-35 minutes or until toothpick inserted into middle comes out clean. Cool brownies completely.
For frosting, beat together 3/4 cup softened butter and powdered sugar with an electric mixer on medium speed. Slowly add milk until frosting consistency. Beat in mint extract and desired amount of green food coloring until well combined. Stir in chocolate, then spread over cooled brownies.
SNAPPY TIPS: Be sure to cool the butter/chocolate completely after melting before adding to batter. Also, be sure to cool the brownies completely before frosting. To easily cut the brownies into squares, refrigerate the brownies for a few hours.SNAPPY SUBSTITUTIONS: Instead of semi-sweet chocolate you could use dark chocolate or bittersweet. Instead of, or in addition to, the vanilla extract in the brownie batter you can use mint extract.
Keywords: brownies from scratch, National Brownie Day, St. Patrick's Day Dessert