I've seen the same cocktail with equal parts amaretto, cherry brandy and vermouth but's a recipe for an overly sweet cocktail – even for a dessert cocktail...
Made this one with blanc vermouth and I thought it was lovely. It's sweet, but not as much as one would expect from Heering and Disaronno together. I'll be coming back to this one if one day I get a bottle of dry vermouth to see the difference.
Another update because I forgot to give one; I think I prefer a blanc vermouth over a dry vermouth for this one. For the blanc vermouth I used Dolin and for the dry vermouth I used Martini, but I wonder how it would go if I used Dolin Dry and Martini Bianco. Maybe in a very distant future I'll try different brands.