Preheat your oven to 350℉. Place 18 paper cupcake liners into three 6-cup or two 12-cup standard size muffin pans. Set aside.
To the bowl of a stand mixer fitted with the paddle attachment (or use a large mixing bowl and electric hand mixer), add butter and sugar. Mix on High speed for about 2 minutes, until smooth and fluffy.
Add eggs and vanilla to the bowl and mix on medium speed to incorporate.
Add the flour, baking powder, salt, and cocoa powder to the bowl. With the mixer on low speed, slowly incorporate dry ingredients, mixing until there are no visible clumps or streaks of flour.
Add the whole milk and mix again until the batter is smooth. Using a silicone or rubber spatula or spoon, gently fold in the crushed Oreo pieces.
Using an ice cream scoop or large spoon, add batter to the prepared pans, filling 18 wells completely with batter. *If you have empty wells, add 1 tablespoon of water to each, to help prevent the pan from warping.
Bake the cupcakes in preheated oven for 25 minutes, or until a toothpick inserted into the center of a cupcake comes out clean or with a few moist crumbs when removed.
Allow the cupcakes to cool completely before decorating with a frosting of your choice. *See recipe notes for frosting ideas.
Notes
Lining your pans with paper liners helps prevent the cupcakes from sticking.
Avoid over mixing the batter, as it can cause cake to be dry and crumbly.
Let the cakes cool completely before decorating.
Easy way to crush Oreos: I crush the cookies in a food processor to make the job quick and easy. Another option is to close the cookies up in a large Ziploc bag, and use a rolling pin to crush them.
Cupcake Frosting and Decorating Ideas
All of these frosting ideas are great with or without sprinkles, jimmies, crushed cookies, or other candies on the top.