Mix in the order: cacao, menthe, whiskey, milk.
Try to keep the layers separate.
Float on the back of a spoon, tilt the glass and pour very gently, etc.
I suggest tilting the glass.
When you tilt the glass you can, when pouring the cream/milk, rotate the glass causing the cream to swirl down through the other layers which looks good.
Serve in an apertif glass.