Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, sift together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed for 2 minutes until smooth.
Stir in the boiling water carefully; the batter will be thin.
Divide the batter evenly between the prepared cake pans.
Bake for 30 minutes or until a toothpick inserted into the center comes out clean.
Remove from oven and allow cakes to cool in the pans for 10 minutes. Then remove cakes from pans and cool completely on wire racks.
To make the Oreo frosting, beat the softened butter on medium speed until creamy, about 2 minutes.
Gradually add the powdered sugar, one cup at a time, beating on low speed until combined.
Add the heavy cream and vanilla extract, then beat on high speed for 3 minutes until fluffy.
Fold in the finely crushed Oreo cookies until evenly distributed.
Place one cake layer on a serving plate. Spread a generous amount of Oreo frosting on top.
Place the second cake layer on top and frost the top and sides of the cake with the remaining Oreo frosting.
Refrigerate the cake for at least 30 minutes before serving to set the frosting.