1. Whisk together flour, corn starch, cocoa powder, and salt.2. With an electric mixer combine butter and sugar until light and fluffy. Add in egg and vanilla and continue to mix until well blended.
3. Combine all dry cupcake ingredients first. Whisk well. Add the milk and oil into the mixture and combine to form a batter.4. Using a small measuring cup, pour batter into the cupcake liner on top of the Oreo cookie. Fill the cupcake liner about halfway to leave room for it to rise.
5. When ready to bake- Preheat the oven to 3506. Carefully slice the dough into ¼- ½ inch slices and place on a baking sheet.7. Bake for 8-12 minutes or until set.8. Remove from oven and allow to cool on the baking sheet for 2-3 minutes, remove to cooling rack to cool completely.