Preheat the oven to 350°F (175°C). Lightly coat a 9 x 13-inch baking dish with nonstick baking spray or line with parchment paper.

In a large mixing bowl, combine the melted butter and granulated sugar. Using a hand mixer or stand mixer, blend the two until the mixture becomes creamy and smooth.

Add the eggs, one at a time, mixing thoroughly after each addition to ensure a uniform batter.

Stir in the vanilla extract, then gradually add the flour. Mix until the flour is just incorporated—avoid overmixing.

Pour in the Hershey’s chocolate syrup, blending until the batter is smooth and well combined.

Transfer the batter to the prepared baking dish, spreading it evenly with a spatula.

Bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). Allow the brownies to cool in the pan for 10–15 minutes before frosting.

In a small saucepan, combine the melted butter, cocoa powder, and 1 tablespoon of milk. Warm over medium heat until the mixture reaches a gentle boil.

Place the powdered sugar in a large mixing bowl. Slowly pour in the warm cocoa mixture, stirring gently to avoid lumps.

Using a mixer, blend the frosting until smooth. Add the vanilla extract, followed by additional milk as needed to achieve a spreadable consistency.

Spread the frosting evenly over the slightly cooled brownies using an offset spatula.

Allow the frosted brownies to cool completely at room temperature. The frosting will firm up to a fudge-like consistency. Once fully set, slice into squares and serve.