Preheat the oven to 350 degrees and line a cupcake pan with 4 paper liners.
In a medium bowl, whisk together the flour, black cocoa powder, 1/2 cup sugar, baking soda, and salt.
Add the buttermilk, vegetable oil, egg, and 1 teaspoon vanilla extract to the dry ingredients. Stir until the batter is smooth and no dry streaks remain.
In a separate small bowl, beat the cream cheese with the remaining 2 tablespoons sugar and 1/2 teaspoon vanilla extract until creamy.
Spoon the chocolate batter evenly into the 4 liners. Drop spoonfuls of the cream cheese mixture on top of each and use a toothpick to swirl it lightly into the batter.
Bake for 18 to 20 minutes until a toothpick inserted in the center comes out clean. Cool the cupcakes in the pan for 5 minutes before moving them to a wire rack.