Take an orange peel and rub it along the rim of a cocktail glass to release its oils and add aroma.
In a cocktail shaker, combine the unsweetened bourbon or rye whiskey, monk fruit simple syrup, and orange bitters.
Add ice to the shaker and shake the mixture well until chilled.
Strain the cocktail into the prepared glass, using a cocktail strainer, to catch any ice or pulp.
Garnish the Keto Old Fashioned with a fresh twist of orange peel. Express the oils from the peel by gently squeezing it over the drink to release its fragrance. Serve immediately.