Preheat the oven to 350. Line 12 wells of a muffin tin with paper liners. Place an Oreo cookie in the bottom of each paper liner, and set aside.
In a large bowl or the bowl of a stand mixer, add the cake flour, all purpose flour, sugar, baking powder, and salt, and whisk to combine. Mix in the butter until the mixture resembles coarse crumbs.
Add the eggs one at a time, mixing after each addition. Combine the milk and vanilla extract in a small bowl or measuring cup, and add half of the milk mixture to the batter. Mix until smooth, then add the other half of the milk mixture and mix until smooth.
Scoop into prepared muffin tin, filling ½-2/3 full. Bake 20 minutes, or until the tops spring back when touched lightly and a toothpick inserted into the center comes out clean. Remove and let cool completely.
After the cupcakes have cooled, beat together the marshmallow fluff and butter until light and fluffy. Add the powdered sugar and vanilla, and add enough cream to make a smooth, easily pipeable frosting. Beat until light and fluffy. Mix in the finely crushed Oreos. Pipe onto the cooled cupcakes (I used a jumbo round tip) and garnish with additional Oreos as desired.