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 of the brownies.
In a medium saucepan over low heat, melt the 10 tablespoons of unsalted butter. Once melted, remove from heat and let it cool slightly.
In a large mixing bowl, combine the melted butter, 1 cup of granulated sugar, and ¾ cup of packed dark brown sugar. Add the ¾ cup + 2 tablespoons of unsweetened cocoa powder, 1 teaspoon of salt, and 1 teaspoon of vanilla extract. Whisk until well combined.
Crack in the 2 large eggs, one at a time, mixing well after each addition. The batter should be smooth and glossy.
Gradually add 1 cup of all-purpose flour to the batter, folding it in gently until just combined. Be careful not to overmix; you want to keep that fudgy texture.
Fold in the 6 oz. of semi-sweet chocolate chips or chunks. This will give your brownies those delightful chocolate bursts throughout.
Pour the brownie batter into the prepared baking pan, spreading it evenly. Bake in the preheated oven for about 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
While the brownies are baking, heat the ½ cup + 2 tablespoons of heavy whipping cream in a double boiler or in the microwave until it just begins to simmer. Remove from heat and add the chocolate hearts and 1 tablespoon of granulated sugar. Stir until smooth and glossy.
Once the brownies are baked, let them cool in the pan for about 10 minutes. Pour the chocolate ganache over the brownies, spreading it evenly with a spatula. Optional: Sprinkle with colorful sprinkles for a festive touch.
Allow the ganache to set at room temperature, or refrigerate for about 30 minutes to firm up. Cut the brownies into squares and enjoy your delicious Fudge Brownies with Chocolate Ganache!
