At the Upper East Side location of Shake Shack, the featured frozen custard topping this month is brown sugar-roasted pineapple. It's as good as it sounds, the sweet and deep flavor of brown sugar completely infused into chopped pineapple. Have it plain and pure with the vanilla custard, or even better, as an added topping to the Coffee Bean Brownie Concrete ($6.50 pictured). Here the vanilla frozen custard gets whipped at high speed with tiny brownie cubes and silky coffee-caramel swirls, all topped off with whipped cream. The addition of the tart pineapple offsets heavier, more intense components of the concrete, and, who would have guessed, coffee and pineapple makes a pretty swell pairing.