Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.

1. Prepare the chocolate cupcake base: In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
2. Add the eggs, milk, oil, and vanilla extract, and mix until the batter is smooth.
3. Gradually add the boiling water to the batter, mixing until well combined. (The batter will be thin, which is normal.)
4. Divide the batter evenly between the 12 cupcake liners, filling each about halfway full.
5. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool in the tin for 10 minutes before transferring them to a wire rack to cool completely.
6. Prepare the cheesecake filling: In a medium bowl, beat the cream cheese and sugar together until smooth and creamy.
7. Add the egg, vanilla extract, and sour cream, and beat until well combined.
8. Once the cupcakes have cooled, use a small spoon or melon baller to make a small indentation in the center of each cupcake.
9. Spoon or pipe the cheesecake filling into each cupcake, filling the indentation to the top.
10. Bake the cupcakes for an additional 12-15 minutes, or until the cheesecake filling is set and the tops are slightly golden.
11. Cool in the tin for 10 minutes before transferring to a wire rack to cool completely.
12. Once cooled, you can garnish with chocolate chips, whipped cream, or fruit if desired. Serve and enjoy!