This is a really delicious fall drink, with sweet, bitter, spice, and tart flavors all mingling happily. My bartender made this for me, and he used either a red or rose Pineau des Charentes, though I'd think white would work as well. I'll clarify next time I go in. I'm not a beer drinker, so I'm not sure how essential the Ephemere is, but the apple flavors do complement the brandy nicely.
Ephemere is a white ale brewed with apples and spices, so I'd imagine it's important to the ultimate flavor profile of the drink. Substitutes might be really good apple cider (from Normandy, if possible).