Prep: Heat oven to 350° & grease either a 9x13-inch baking pan or two 8-inch baking pans (I prefer the 9x13).

Prepare batter: Stir together cocoa and baking soda in a large bowl. Stir in 1/3 cup of the melted butter. Add boiling water & stir until mixture thickens. Stir in sugar, eggs, & remaining 1/3 cup butter until smooth. Add flour, vanilla, & salt. Blend until well-combined. Stir in chocolate chips & pour into prepared pan.

Bake: Bake for 35-40 minutes (9x13) / 30-35 (8x8) or until brownies begin to pull away from the sides of the pan. Cool completely in pan on wire rack.

Frost: Once brownies are cool, make the buttercream frosting. Beat butter in a medium bowl. Add powdered sugar & cocoa alternately with milk, beating to spreading consistency. Additional milk may be needed to reach desired consistency. Stir in vanilla extract. Garnish with additional chocolate chips.