Genever is a Dutch spirit typically made from a mixture of malted barley, wheat, corn and rye that's flavored with juniper and often aged in oak casks. Philip Duff describes it as being "close to good whiskey."
Fill a pint glass with ice. Add the genever and elderflower liqueur and stir well. Strain into an ice-filled rocks glass. Pinch the lemon twist over the drink, rub it around the rim of the glass, then drop it into the drink.