Cream, chocolate and liqueur go into the bowl together. Chocolate seizes when a small amount of liquid meets it, so melting it first and adding the cream afterwards is how it turns to stiff paste. If it does seize, stir in more warm cream until it comes back.
The bowl must not touch the water. Steam is doing the melting; direct contact takes the chocolate too hot.
Milk chocolate is not swappable for dark weight for weight. Dark carries far more cocoa solids and far less sugar, so the same amount sets much firmer and can split. Use about a third less if you want it darker.
Beat the cream cheese smooth on its own first. Lumps will not come out once the cream is in, and the mixture goes from stiff peaks to grainy in seconds.
Go carefully with the butter in the base. Too much and it sets hard in the fridge and you cannot get a spoon through it.
Chilling: 20 minutes a layer will set them enough to eat, but a few hours or overnight is noticeably better, because the coffee mellows into the cream. Dust the cocoa on just before serving - left on overnight it draws moisture from the cream and goes patchy.
Keeping them: two to three days in the fridge, covered. Do not freeze; the cream cheese layer comes back grainy.