Preheat your oven to 350°F (175°C) and prepare two 9-inch cake pans by lining with parchment paper and greasing the sides.

Melt about 8 ounces of chopped dark chocolate in a microwave-safe bowl or double boiler until smooth. Allow to cool slightly.

In a large mixing bowl, beat ½ cup unsalted butter, ¾ cup granulated sugar, and ¾ cup light brown sugar until light and fluffy.

Add eggs one at a time and mix well. Pour in 2 teaspoons vanilla extract and mix until incorporated.

Slowly pour in the slightly cooled melted chocolate and mix until smooth.

In a separate bowl, whisk together 1 ¾ cups flour, ¾ cup cocoa powder, 1 teaspoon baking soda, 1 teaspoon baking powder, and ½ teaspoon salt. Add 1 teaspoon espresso powder if using.

Gradually add dry ingredients to the wet mixture in three alternating batches, starting with dry and then 1 cup buttermilk, mixing until just combined.

Gently fold in 1 cup semi-sweet chocolate chips into the batter.

Divide batter evenly between prepared cake pans and bake for 30-35 minutes until a toothpick comes out with moist crumbs.

Cool cakes in pans for 10 minutes, then transfer to wire racks to cool completely.

To make ganache, heat 1 cup heavy cream until simmering, pour over 8 ounces chopped dark chocolate, let sit, stir until smooth. Add 2 tablespoons butter and mix.

Once cooled, assemble the cake by layering ganache and placing the second cake on top, pouring remaining ganache over the top.