Step 1: Preheat Oven and Prepare Pan : Preheat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper or lightly grease it.

Step 2: Melt Butter and Chocolate : In a medium saucepan, melt butter and chopped semi-sweet chocolate over low heat, stirring until smooth and combined. Remove from heat and let it cool slightly.

Step 3: Prepare Brownie Batter : Stir in sugar until smooth. Add eggs, one at a time, mixing well after each addition. Stir in vanilla extract. In a separate bowl, whisk together flour, cocoa powder, and salt. Gradually fold the dry ingredients into the wet mixture until fully incorporated.

Step 4: Add Chocolate Chips and Chunks : Gently fold in milk chocolate chips and dark chocolate chunks. Pour the batter into the prepared baking pan and spread evenly.

Step 5: Bake the Brownies : Bake in preheated oven for 30–35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Avoid overbaking to maintain fudgy texture. Remove from oven and cool completely in the pan.

Step 6: Prepare the Cocoa Frosting : In a medium bowl, beat softened butter until creamy. Gradually add powdered sugar and cocoa powder, beating until smooth. Add vanilla extract, a pinch of salt, and milk, one tablespoon at a time, until desired spreading consistency is achieved.

Step 7: Frost and Serve : Once the brownies have cooled completely, spread the cocoa frosting evenly over the top. Optionally, sprinkle extra chocolate chips or shaved chocolate on top for decoration. Cut into 16 squares and serve.