This is a modified version of a classic cocktail that I found in Imbibe! and promptly fell in love with, the Prince of Wales Cocktail. In terms of construction, it's similar to one of our current best-selling cocktails (though stripped-down for speed) and thus fills the bubbly cocktail slot on our menu nicely.
3/4 oz rye whiskey
1/2 oz pineapple juice
4-5 dashes ras-el-hanout bitters
4 oz brut cava
Drop a sugar cube into a champagne flute and soak with the bitters; add a little ice, top up with whiskey, and then cava.
I don't think this really needs any more explanation - it's a remarkably simple drink which successfully marries the luxurious flavor of the Prince of Wales with the crispness of a champagne cocktail.