Preheat oven to 350F and line two 12-count regular muffin pans with paper or foil liners. I made 22 cupcakes and you could probably get 24 from the batch if you fill them more shallow; and the recipe halves easily if you need 11-12 cupcakes. Set pans aside.
To a large bowl, add the milk, apple cider vinegar, stir, and set aside for about 5 minutes to curdle. It doesn’t get as thick as regular buttermilk and that’s okay.
While waiting for the milk, to a separate large bowl, add the sugar, oil, vanilla, and whisk a bit. Mixture is thick and granular.
Add the curdled milk to the sugar-oil mixture and whisk until smooth and combined; set aside.
To a separate large bowl, add the flour, cocoa, baking soda, baking powder, salt, and whisk to combine.
Slowly add the wet mixture to the dry, stirring until smooth and no large lumps remain. A few tiny lumps are okay. Don’t overmix because that can result in tough cupcakes.
Turn batter out into prepared muffin pans, filling each cavity to about 3/4-full.
Bake for about 20 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs, but no batter, and are domed and springy to the touch. Start watching closely and checking at 17-18 minutes since all ovens and climates vary; don’t overbake which is easy to do with dark-colored items.
Allow cupcakes to cool in pan for 5 to 10 minutes before removing and placing on a wire rack to cool completely.
After cupcakes have cooled completely they can be frosted.
Frosting
To a stand mixer fitted with the paddle attachment (or large mixing bowl and electric mixer), add the butter, confectioners’ sugar, and beat on low speed for about 2 minutes before increasing to high speed and beating for about 3 minutes, or until very light and fluffy; set aside.
Roughly chop the Oreos. I chop by hand because I like some decent-sized pieces of Oreos rather than having them pulverized into crumbs which is what tends to happen all too quickly in the food processor.
Add the Oreos to the frosting and mix on low speed until just incorporated, about 30 seconds.
Frost each cupcake with a generous dollop of frosting. I used my 2-tablespoon cookie scoop but you can experiment with what works best.
Notes
Frosting recipes makes enough to generously frost each cupcake (about 2 heaping tablespoons per cupcake) and any extra will keep airtight for weeks in the fridge. Make ahead option: Cupcakes can be made the night before or a day in advance if necessary and stored airtight at room temp before frosting them. Storage: Cupcakes are best fresh, and I am okay with storing frosted cupcakes at room temp for a day or two but if you’re not, store airtight in the fridge, noting cupcakes will dry out much quicker in the fridge than at room temp.Cupcake recipe generously adapted from Vegan Cupcakes Take Over the World; frosting recipe is my own.