Step 1: Make the Brownies : Preheat oven to 350°F (175°C). Grease and line an 8x8-inch baking pan with parchment paper. In a large bowl, whisk together melted butter, sugar, eggs, and vanilla extract until smooth. Add cocoa powder, flour, salt, and baking powder. Stir gently until combined — don’t overmix. Pour batter into the prepared pan and smooth the top. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Let the brownies cool slightly, then cut into squares.

Step 2: Make the Hot Fudge Sauce : In a medium saucepan, combine heavy cream, brown sugar, cocoa powder, and salt. Bring to a gentle simmer over medium heat, whisking constantly. Add chocolate chips and whisk until melted and smooth. Stir in butter and vanilla extract. Simmer for 2–3 minutes until the sauce thickens slightly. Remove from heat and let cool for 5–10 minutes (it will thicken more as it cools).

Step 3: Assemble the Sundaes : Place a warm brownie square in a dessert bowl or glass. Add one or two scoops of ice cream on top. Drizzle generously with hot fudge sauce. Top with whipped cream, nuts, caramel drizzle, or a cherry for extra flair.