The doyenne of all ice cream parlors. Here it was that the knickerbocker glory was first introduced to England in the 1950s (they say, although Wikipedia is not so sure). Book a table, first floor. There are coupes and floats and a menu from pomegranate to elderflower plus sauces to overlay plus toppings. Two scoops £7.75, sauce 50p, topping 90p, all served in the calm of the Parlour. The knickerbocker itself was in fact a Manhattan hotel garishly decorated in pink and knocked down in the 1920s. See here for review of the rest of the shop.
1st floor, Fortnum & Mason, 181 Piccadilly, London W1A 1ER