Preheat your oven to 350°F (175°C). Lightly grease and flour a 9x5 inch loaf pan, or line it with parchment paper leaving an overhang on the long sides for easy removal.

In a medium bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. Set aside.

In a large mixing bowl, combine the melted butter, granulated sugar, and light brown sugar. Use an electric mixer to beat until well combined and slightly lightened in color (about 1-2 minutes).

Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients in three additions, alternating with the buttermilk in two additions. Begin and end with the dry ingredients. Mix on low speed until just combined, being careful not to overmix. A few streaks of flour are fine.

Gently fold in the 1/2 cup of chocolate chips with a rubber spatula.

Pour the batter evenly into the prepared loaf pan. Bake for 50-60 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out with moist crumbs, but no wet batter. If the top browns too quickly, you can loosely tent it with foil during the last 15-20 minutes of baking.

Let the cake cool in the loaf pan for 10-15 minutes before carefully lifting it out by the parchment paper overhang (if used) or inverting it onto a wire cooling rack to cool completely. The cake must be completely cool before adding ganache.

Place the chopped dark chocolate or chocolate chips in a heatproof bowl.

In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer around the edges (do not boil).

Pour the hot cream over the chocolate. Let it sit for 5 minutes without stirring, allowing the chocolate to melt. Then, whisk gently from the center outwards until the ganache is smooth and glossy.

Stir in the optional unsalted butter for extra shine. Let the ganache sit for another 5-10 minutes to thicken slightly, or until it reaches a pourable but not runny consistency.

Once the cake is completely cool, pour the chocolate ganache over the top, allowing it to drip down the sides. You can use a spatula to gently spread it if desired. Let the ganache set for at least 30 minutes at room temperature before slicing and serving.