01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper.
02 - Melt butter and semisweet chocolate chips together in a heatproof bowl over simmering water, stirring until smooth. Remove from heat.
03 - Whisk in granulated sugar, then add eggs one at a time followed by the vanilla extract.
04 - Gently fold in flour and salt until just combined, taking care not to overmix.
05 - Pour batter into the prepared pan, smoothing the surface. Bake for 25 to 30 minutes or until a toothpick inserted in the center comes out with moist crumbs. Cool completely in the pan, then cut into six squares.
06 - Combine heavy cream, semisweet chocolate chips, unsalted butter, and corn syrup in a saucepan over medium heat. Stir continuously until melted and smooth. Remove from heat and stir in vanilla extract and a pinch of salt.
07 - Place one brownie square in each serving bowl. Top with a generous scoop of vanilla ice cream, drizzle with hot fudge sauce, then garnish with whipped cream, nuts if desired, and a maraschino cherry.