If I could only drink one cocktail this would be it and I am well on the way to developing a repetitive strain injury due to all the stirring. Unfortunately the time it takes to make one means that it does not feature on many bar cocktail lists, but any barman worth his salt will make you one as long as the bar is not too busy.
From what I can determine Woodford Reserve is generally accepted as the recommended bourbon for this, but Four Roses is also good. When short of cash I have used the Sainsbury’s brand Kentucky Bourbon and enjoyed the drink at the end of it so no need to be a brand Nazi.