Preheat the oven to 350°F (177°C).

Line a 9x13-inch baking pan with parchment paper and lightly coat with nonstick cooking spray.

Add the melted butter, granulated sugar, and vanilla to a large mixing bowl.

Whisk until smooth and thoroughly combined.

Add the eggs and whisk until the mixture is smooth.

Add the flour, cocoa powder, and salt.

Fold the dry ingredients into the wet mixture just until combined. The brownie batter will be quite thick.

Spread the batter evenly in the prepared baking pan, smoothing the surface.

Bake for 24–30 minutes. For fudgier brownies, remove them when the center is mostly set but still slightly soft. For firmer brownies, bake until a toothpick inserted near the center comes out with only a few moist crumbs.

Transfer the pan to a cooling rack and let the brownies cool before slicing.

Cut into 12 large brownies or smaller portions if preferred.

To assemble a Brownie Sundae, place one brownie on a dessert plate or in a shallow bowl.

Top with a generous scoop of ice cream.

Drizzle with thick chocolate sauce.

Sprinkle mini chocolate chips over the top.

Add whipped cream, chopped peanuts, sprinkles, or a cherry if desired.

Serve immediately before the ice cream melts.