Preheat your oven to 350°F (175°C). Grease your 9x9-inch baking pan with butter or line it with parchment paper for easy removal.
In a medium saucepan over low heat, melt the 10 tablespoons of unsalted butter. Once melted, remove it from the heat and let it cool slightly.
In a large mixing bowl, combine the granulated sugar, dark brown sugar, and cocoa powder. Whisk until well combined.
Pour the melted butter into the sugar mixture, followed by the salt, vanilla extract, and eggs. Whisk until the mixture is smooth and glossy.
Gently fold in the all-purpose flour until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Add the 6 oz. of semi-sweet chocolate chips or chunks to the brownie batter. Use a rubber spatula to fold them in evenly.
Pour the brownie batter into your prepared pan, spreading it evenly. Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
While the brownies are baking, prepare the chocolate ganache. In a double boiler or microwave, combine the 6 oz. of semi-sweet chocolate with 1/2 cup + 2 tablespoons of heavy whipping cream, 1 tablespoon of granulated sugar, and 1 tablespoon of corn syrup. Stir until smooth and glossy.
Once the brownies are baked, let them cool in the pan for about 10 minutes. Then, carefully lift them out and transfer them to a cooling rack. Once completely cool, pour the ganache over the brownies, spreading it evenly.
Place the 9 Hershey's Chocolate Hearts in a decorative pattern on top of the ganache, and sprinkle with colorful sprinkles for a festive touch.
