In a medium bowl, whisk together the flour, cocoa powder, granulated sugar, baking powder, baking soda, and kosher salt. Set aside.
In a separate medium bowl, whisk together the buttermilk, egg, melted butter, and vanilla extract until smooth. Pour the wet ingredients into the dry ingredients. Whisk until just combined. The batter will be slightly lumpy; do not overmix.
Let the batter rest for 5 to 10 minutes while you preheat your skillet or griddle.
Spray a large nonstick skillet or griddle with nonstick cooking spray and heat over medium-low heat, about 300°F.
When the surface is hot, pour ⅓ cup of batter onto the skillet. Gently spread it out into a 4 to 5 inch circle.
Cook for 3 to 4 minutes, or until bubbles begin to form and pop on the surface.
Carefully flip the pancake and cook for an additional 3 to 4 minutes, or until fully cooked and no longer doughy in the center.
Repeat with remaining batter, working in batches. Wipe the skillet with a paper towel between batches to prevent sticking.
Serve warm with your favorite toppings.