How to Make It
In a small saucepan, toast the cardamom, peppercorns and cinnamon over moderate heat until fragrant, about 2 minutes. Add 1 cup of water and bring to a boil. Remove from the heat and let stand for 15 minutes. Stir in the sugar and cocoa powder and return to a simmer. Cook for 5 minutes over low heat. Cool the syrup, then strain it into a glass jar or plastic container.
For each soda: In a tall ice-filled glass, stir 1/4 cup of the syrup with 1 tablespoon of cream and a pinch of citric acid. Top with seltzer, stir and serve right away.
The chocolate syrup can be refrigerated for up to 1 month.
Citric acid is available at vitamin shops, well-stocked grocery stores and online at williams-sonoma.com.