Line a baking pan with parchment paper. Leave some extra paper beyond the top of the pan to make it easy to remove the finished cake. Since this no-bake pudding cake gets its shape from the container you put it in, you can make it in a variety of shapes; I used a 9” x 5” loaf pan for a rectangle shape, but you could easily use a Bundt pan or circle pan instead for a different shape.
Make the base:
Crush the 11 Oreos. You can use a food processor or put them in a Ziploc bag and smash them with a rolling pin or a serving spoon.
Mix the crushed Oreos with the 4 tablespoons of melted butter.
Reserve ¼ cup of the crushed Oreo and butter mixture to use in the next layer.
Press the remaining Oreo and butter mixture into the bottom of the baking pan in an even layer using a spoon or the bottom of a glass.
Put the pan in the freezer for 15 minutes.
Make the Milo Layer and the Oreo + Milk Layer:
Combine 1 ½ packets of gelatin powder, ½ cup sugar, salt, and cornstarch in a pot. Stir well. Pour in the whole milk and stir well again.
Cook over medium heat until boiling, stirring often. Boil for 1 minute.
Split it in half across two bowls.
In the first bowl, add the ¼ cup Oreo mixture from earlier. Cover the other bowl to keep it warm for later.
Crumble the remaining 2 Oreos into large chunks and add to the first bowl.
Spoon the contents of the first bowl carefully on top of the Oreo base.
Refrigerate for 1 hour or until mostly set. The surface should be solid and slightly sticky to the touch.
In the second bowl, add the Milo, stir well, and spoon it carefully on top of the Oreo layer. It should sit on top of the Oreo layer- if it doesn’t, wait longer for the Oreo layer to set.
Refrigerate for 1 hour or until mostly set. Again, the surface should be solid and slightly sticky to the touch.
Make the Chocolate layer:
Mix all ingredients in a pot.
Cook over medium heat until boiling, stirring often.
Spoon the chocolate layer carefully over the Milo layer. It should sit on top of the Milo layer if it doesn’t, continue chilling until the Milo layer is set.
Refrigerate until fully set, about 2 hours.
Carefully lift it out of the pan using the parchment paper edges.
Slice and serve. Store in the refrigerator for up to 3 days.