Crushed cookie layer:

1. Add the cookies and melted butter (if using) to a food processor. Blitz until they form a fine crumb. Set aside

Chocolate pudding layer:

1. Add the heavy cream, milk, vanilla and salt to a saucepan. Heat on low flame until the mixture starts to simmer
2. In a bowl, whisk the eggs, egg yolks and sugar until combined
3. Pour the hot milk mixture into the egg mixture while whisking continuously. This step helps temper the eggs so they don't cook or curdle
4. Pour the entire mixture back into the saucepan. Cook and stir on a low flame for ~8-10 minutes until the mixture thickens like a custard and coats the back of a spoon. Make sure to keep stirring so the mixture doesn't stick or curdle. Once it starts to boil, it will thicken quickly. Be careful not to overcook or overthicken as the custard can split
5. Add the milk and dark chocolates into 2 separate bowls. Pour half of the hot custard onto each bowl, passing it through a fine sieve mesh to get rid of lumps. Let sit for 5 minutes, then gently stir to melt the chocolates into the custard and form the dark and milk chocolate puddings. If you see any bits of unmelted chocolate, microwave for 10-20 seconds and stir again 
6. Place the puddings in the fridge for ~30 minutes so they can thicken up. This will allow for neater layering during assembly 

Whipped cream layer:

1. Whisk the heavy cream, vanilla and sugar until the mixture thickens up and reaches the "medium peak" stage. Do not over whisk
2. Transfer the whipped cream to a piping bag - this will make it easy to spread

Ganache:

1. To make the ganache, add the cream, chocolate and oil to a microwave safe bowl. Microwave in 20 second increments, stirring between each, until a smooth chocolate ganache forms. Keep it at room temperature

Assembly:

1. When the puddings have cooled down, it's time to assemble!
2. In a trifle bowl, add half of the crushed cookies and gently press down with the bottom of a glass or measuring cup. Then add all of the dark chocolate pudding and spread it out. Pipe on half of the whipped cream and spread it evenly, taking care to keep the edges as neat as possible. Repeat this process, with a layer of the remaining crushed cookies, all of the milk chocolate pudding and the remaining whipped cream. You can also add more layers (e.g., 3 layers of each component instead of 2)
3. Refrigerate the trifle for 6-8 hours until it is thoroughly chilled
4. When ready to serve, remove from the fridge. Warm the ganache for a few seconds until it is runny. Pour over the trifle and spread it out. Decorate with cherries and chocolate shavings
5. Serve & enjoy!

Video Tutorial: