Bourbon, ginger beer, and fresh lime in a copper mug — the American Mule, and some say the better one.
The Kentucky Mule is a Moscow Mule (vodka, ginger beer, lime) made with bourbon instead of vodka. The switch originated in Kentucky bars where bourbon was the obvious spirit of choice, and the combination turned out to work extremely well — bourbon's caramel, vanilla, and spice notes play beautifully against ginger heat.
Many experienced cocktail drinkers prefer the Kentucky Mule to the Moscow Mule precisely because bourbon isn't neutral — it contributes flavour rather than just alcohol. The key is using a quality ginger beer (never ginger ale, which is too sweet and lacks the heat). Fever-Tree Original Ginger Beer is the most widely available good option.
Use a 6-year aged bourbon for more complexity. The extra age adds more tannin and vanilla that stands up to the ginger beautifully.
Use rye whiskey instead of bourbon for a drier, spicier version. The pepper in the rye amplifies the ginger heat.
Add ½ oz peach schnapps or peach liqueur (Mathilde Pêche). The sweetness rounds out the spice and adds a Southern warmth.