Add the chopped chocolate to a heat proof bowl. Microwave for 45 seconds on medium power (not high/regular power or the chocolate will burn), remove from the microwave and stir. Repeat the process until the chocolate is melted.
In a large bowl, beat the heavy cream until stiff peaks form and you have whipped cream.
In a separate large bowl, beat the cream cheese until soft. Then beat in the melted chocolate and powdered sugar.
Gently fold the whipped cream into the cream cheese mixture until smooth.
Spread 1-2 tablespoons of the chocolate filling onto the bottom of an 8x8 inch pan.
Gently dunk each Oreo cookie in the milk, shake off the extra milk, and place in a layer on the bottom of the pan with 4 rows of 4 cookies.
Spoon the rest of the chocolate filling over top, and smooth.
Gently dunk the rest of the Oreos in the milk and place a layer on top of the chocolate filling, pressing the cookies down gently.
Place in the fridge as you make the topping.
Topping
Beat the cream and powdered sugar until stiff peaks form.
Spread the whipped cream over top of the icebox cake and sprinkle with chopped Oreos.
Place in the fridge to set for at least 6 hours before serving.
Notes
Heavy cream/whipping cream can be substituted with thawed Cool Whip. If using Cool Whip, you do not need to add powdered sugar to the topping (but still use powdered sugar in the chocolate filling).
The milk DOES NOT go into the chocolate filling. It is only used to dunk the Oreo cookies in. Dunking the Oreo cookies in milk is necessary so that the cookies soften and you can slice the cake.
Recipe can be doubled and made in a 9x13 inch pan.
Store the cake covered in the fridge for up to 4 days.