The crunch is Viennese crunch, no recipe, ya gotta buy it. it is a combination of chopped almond or hazelnut-covered toffee, I guess. So if you are of a mind to make your own toffee and cover it with chopped nuts, I think you’re better off buying it ready made. Some people use Heath Bars (?), but whatever it’s called, I think those are milchig.
I actually used to use a Duncan Hines mix, because the trifle assembly takes time, and it was just one less thing to do. I used to have an amazing from scratch devil’s food cake that I made for many years, but the DH cake mix tasted almost exactly like it, and I potchked with enough things that I cooked and baked from scratch, that this didn’t have to be one of them. The irony is that nowadays I have to do everything for my family from scratch again, because of a severe allergy to nuts and seeds that a family member has, so I cannot use most of the prepared mix items.