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 eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed for 2 minutes until well combined.
Stir in the boiling water carefully; the batter will be thin.
Divide the batter evenly between the prepared cake pans.
Bake for 30 to 35 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 turn out onto wire racks to cool completely.
To prepare the Oreo frosting, beat the softened butter on medium speed until creamy, about 2 minutes.
Gradually add the powdered sugar and cocoa powder, beating on low speed until combined.
Add heavy cream and vanilla extract and beat on high speed for 3 minutes until light and fluffy.
Fold in the finely crushed Oreo cookies gently with a spatula.
Place one cake layer on a serving plate and spread a thick layer 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.