In a bowl, add flour, baking soda, baking powder, cocoa powder, salt, cornstarch, and both sugars. Stir everything together.
In a separate bowl, combine milk mixture with eggs, oil, mayo, and vanilla extract. Whisk to combine.
Add wet ingredients to dry ingredients.
When the mixture is halfway mixed, add in the warm water.
Once everything is fully mixed, use a medium sized cookie scoop to scoop the batter into cupcake liners, about 2/3's of the way full.
Bake for about 18-22 minutes, then let cool.
While the cupcakes cool, make the frosting.
Making the Frosting.
Crush up chocolate sandwich cookies** until you get about a cup of cookie crumbs.
Add heavy cream to a bowl, and mix on medium speed until you get soft peaks.
Add in vanilla and powdered sugar.
Whip for another minute.
Add in cookie crumbs and use a spatula to fold in gently.
Add frosting to a large piping bag and pipe a large dollop on top of the cupcakes.
Add a few more cookie crumbs and enjoy!
Notes
**If you are using a piping bag for this frosting, you'll want the cookie crumbs to be super small with no big chunks or it'll block up the piping bag!! I suggest maybe using a blender or food process to really get good cookie crumbs!