Combine the dark rum, overproof rum, lime juice, grenadine and absinthe in a shaker.
Add ice and shake hard for 10 seconds.
Strain into a collins glass filled with fresh ice.
Top with cold soda water.
Garnish with a lime wheel and a mint sprig.
Named for Dr. Bernard Funk, a physician in Samoa who reportedly mixed absinthe with grenadine and soda for Robert Louis Stevenson. Don the Beachcomber added the rum and put it on his first menu — arguably the drink that started tiki.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Doctor Funk.