In a small bowl, whisk together the buttermilk, butter, brown sugar, granulated sugar, vanilla and eggs until smooth. In a separate medium bowl, whisk together the flour, cocoa, baking powder, espresso powder and salt. Add the wet ingredients to the dry ingredients and whisk until just combined. Fold in the chopped chocolate, cover and let rest for 15 minutes.
Line a baking sheet with parchment paper. Heat a large nonstick saute pan or cast-iron griddle over medium heat and brush with clarified butter. Once the butter begins to shimmer, drop 1/4 cup of the batter per pancake onto the hot pan. Cook until bubbles start to form, about 2 minutes. Flip and cook another 1 to 2 minutes. Place the pancakes in a single layer on the prepared baking sheet and keep warm in the oven until ready to serve.