For the Cupcakes:

1. Preheat oven to 160°C/320°F. Line a 12-cup muffin tin with paper liners.
2. Boil water and set aside to cool slightly while preparing other ingredients.
3. In a large bowl, whisk together all dry ingredients until well combined.
4. In another bowl, whisk together sour cream, oil, eggs, vanilla, and the slightly cooled boiling water.
5. Pour wet ingredients into dry ingredients and gently stir until just combined. Don’t overmix.
6. Divide batter evenly among cupcake liners, filling each about 2/3 full.
7. Bake for 20-23 minutes, or until a toothpick comes out clean.
8. Cool in pan for 5 minutes, then transfer to a wire rack to cool completely.

For the Oreo Buttercream:

1. Process Oreo cookies in a food processor until they form fine crumbs. Set aside.
2. Beat butter with an electric mixer for 4 minutes until light and fluffy.
3. Gradually add powdered sugar, beating on low speed until incorporated.
4. Add vanilla and milk, beating until smooth.
5. Fold in Oreo crumbs until evenly distributed.
6. Transfer to a piping bag fitted with your favorite tip.

Assembly:

1. Pipe buttercream onto cooled cupcakes.
2. Top with whole Oreo cookies and additional crumbs as desired.