Prepare the Muffin Batter

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, salt, granulated sugar, and brown sugar.
3. Combine Wet Ingredients: In another bowl, mix the buttermilk, vegetable oil, egg, and vanilla extract until well combined.
4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring until just combined. If desired, fold in the chocolate chips.

Prepare the Cheesecake Filling

1. Mix the Cheesecake Filling: In a separate bowl, beat the softened cream cheese, granulated sugar, egg, and vanilla extract until smooth and creamy.

Assemble the Muffins

1. Fill Muffin Liners: Spoon a tablespoon of muffin batter into each muffin liner, followed by a tablespoon of cheesecake filling, then top with another tablespoon of muffin batter.
2. Swirl the Batter: Use a toothpick or knife to gently swirl the cheesecake filling into the muffin batter for a marbled effect.

Bake the Muffins

1. Bake: Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
2. Cool: Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.