Before you start this dessert, go check that you actually have space in your freezer for a 8x8 square dish or 9 inch round pan.
Using a hand mixer or a stand mixer with the whisk attachment, beat the condensed milk with the whipping cream until you obtain a thick and uniform cream, about 3 to 5 minutes. Reserve. (Start by using low speed and as the cream thickens, increase the speed to prevent splattering.)
Stir the milk and coffee together. Set it aside. (I used 1 teaspoon of Nescafe mixed with 120 ml of water for the coffee, but you can prepare the coffee according to your preference.)
In a dish, spread a thin layer of the cream on the bottom. Place a layer of Maria cookies soaked in the coffee-milk mixture on top. Then, add another layer of the cream from the mixer. Alternate the layers until you run out of ingredients. Set it aside (or place it inside your freezer).
In a small saucepan, combine the milk, cocoa powder, sugar, and butter. Bring to medium heat, stirring constantly until you achieve a chocolate cream consistency, about 8-10 minutes.
Be careful not to overcook the chocolate sauce; if it becomes too thick, it may harden excessively when frozen. Pour the chocolate cream over the reserved cake and place it in the freezer for at least 3 hours.