Elderflower liqueur sometimes called bartenders ketchup for how often its brought in to pump up a drinks flavors can sometimes overwhelm other delicate flavors in a drink. Not so here, where inventor jean tomaro of chicagos hogshalt hospitality tames it with the summery flavor of aperol. You can use campari, if you prefer a more bitter flavor, but it wont taste as much of a sun-melted grapefruit candy as the original recipe does.