Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, allowing some overhang for easy removal later.
In a medium saucepan, melt the 3/4 cup of unsalted butter and the 5 ounces of finely chopped semisweet chocolate over low heat, stirring continuously until smooth and fully combined. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the granulated white sugar, light brown sugar, and eggs until the mixture is light and fluffy. This should take about 3-5 minutes.
Gradually pour the slightly cooled chocolate mixture into the egg mixture, whisking continuously to prevent the eggs from cooking. Add in the vanilla extract and mix until well combined.
Sift together the all-purpose flour, cocoa powder, and salt in a separate bowl. Gently fold the dry ingredients into the chocolate-egg mixture using a spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Fold in the 3/4 cup of semisweet chocolate chips, ensuring they are evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan and smooth the top with your spatula. Bake in the preheated oven for 25-30 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 small saucepan, heat 1/2 cup of heavy cream over medium heat until it begins to simmer. Remove from heat and add in 6 ounces of semisweet chocolate chips. Let it sit for a couple of minutes, then stir until smooth and glossy.
Once the brownies are baked, remove them from the oven and allow them to cool in the pan for about 10 minutes. Use the parchment paper to lift them out onto a wire rack. Once cooled, pour the chocolate ganache over the top, spreading it evenly. Let it set for about 30 minutes before slicing into squares.
