White rum, maraschino, lime, and grapefruit — no sugar. The Papa Doble from El Floridita, Havana.
Ernest Hemingway spent 22 years in Cuba and became a fixture at El Floridita bar in Havana, where he drank so many Daiquiris that bartender Constantino Ribalaigua Vert created a special version for him. Hemingway was diabetic and avoided sugar, so the bartender replaced the syrup with maraschino and grapefruit juice.
The 'Papa Doble' (Papa's Double) referred to Hemingway's habit of drinking two at a time. The standard recipe uses double the rum of a classic Daiquiri. The grapefruit and maraschino together replace the sweetness of simple syrup while adding complexity — the drink is drier, more sophisticated, and harder to stop drinking than its three-ingredient cousin.
Add ¼ oz simple syrup if the drink is too dry. The result is closer to a classic Daiquiri with added complexity.
Increase grapefruit to ¾ oz and reduce lime to ½ oz. More citrusy and pink, with the maraschino receding to background sweetness.
Add ½ oz coconut water and reduce grapefruit to ¼ oz. A tropical nod that Hemingway's Cuba days might have approved.