1 pound sweet cherries, pitted and halved (about 3 cups)
3/4 cup sugar
1 vanilla bean, seeds scraped
2 cups water
1 liter seltzer, lemon-lime soda, Coke, or Pepsi
Stir the cherries, sugar, vanilla bean pod and its seeds, and water together in a medium high-sided saucepan. Bring to a boil over medium heat, then reduce the heat to medium-low and simmer for 30 minutes.
Strain the syrup through a fine mesh strainer into a heat-proof lidded container like a Mason jar. Cool to room temperature or refrigerate until cold.
To serve, stir 2 tablespoons syrup into each 8-ounce glass of seltzer or soda, then add more if you prefer.