In a mixing glass, muddle orange slice, cherry, sugar, bitters and a little soda water: using a muddler, push around and break up cherry and orange until flavor is released.
Add soda water so cherry is wet and sugar is melted. Add bourbon or rye and serve over rocks, if desired.
Bourbon or rye may be used in the Old Fashioned. Rye was originally used, and The Grand Central Oyster Bar is starting to use rye again in these drinks; they use Michters', but Don would likely choose Canadian Club, the brand we often see in his office and home. Seagrams V.O. and Crown Royal were also popular in the 1960s, says Jonathan Rogers of The Grand Central Oyster Bar.
Recipe from The Unofficial Mad Men Cookbook: Inside the Kitchens, Bars, and Restaurants of Mad Men by Judy Gelman and Peter Zheutlin (Smart Pop, 2011).