Heat Heavy Cream, Milk, and Sugar - In a medium saucepan, mix the milk and sugar with 1 3/4 cups of heavy cream. Let the mix reach a simmer on low heat, stirring occasionally for around 12 minutes.
Sift the Dry Ingredients - Using a fine sieve, sift the cornstarch and cocoa powder into a medium bowl. Next, whisk the eggs into the mixture and add the rest of the heavy cream.
Combine the Hot Milk Mixture With the Cocoa Powder Mixture - Whisk together the hot milk mixture and the cocoa powder mixture. Cook the mixture over low heat, stirring regularly, for about 30 minutes.
Add Chopped Chocolate - Place your chopped chocolate into a medium heat-proof bowl and place a fine sieve over it. Strain your pudding using the fine sieve into the bowl. Let it sit for three minutes, then whisk until smooth. Next, add the butter and salt and whisk together.
Place plastic wrap over the bowl and place in the fridge for about three hours.
Prepare the Whipped Cream - With a hand mixer, beat the heavy cream, confectioners’ sugar, vanilla, and salt in a medium bowl for about five minutes.
Assemble the Trifle - In your trifle bowl, add a layer of pudding, whipped cream, and then Oreos. Repeat four times and serve.