Modern cognac drowns here, but blended scotch creates a remarkably vibrant combination worth community exploration. Our best effort has been the Treaty of Lyon (a nod to Savoy), a drier 2/1/1 ratio of scotch, Fernet, and creme de cacao, finished with a touch of vermouth and Islay malt (flamed orange optional). A bit of fine-tuning yields a remarkable result.
Good idea re. whiskey, works very well. Had to push the dilution a bit further than the initial shake: as you say when you hit the sweet spot the results are remarkable.