Use a paper clamp to tightly fasten a medium (No. 4) paper cone coffee filter onto the inside rim of a glass or plastic pitcher that can hold at least 2 quarts. Place cacao nibs in the filter.
Pour about 1 cup water over the nibs until they are completely saturated, letting the liquid drip into the pitcher. Carefully unclip the filter; gently fold it over at the top and seal it with string or a rubber band (so no nibs can escape), then drop it directly into the pitcher. Pour in an additional 7 cups water.
Cover, and let the nibs steep at room temperature for 12 to 14 hours. Discard the nibs; refrigerate the cold-brewed chocolate until well chilled (and up to 1 week).
For each serving, measure 8 ounces (1 cup) cold-brewed chocolate into a 12-ounce glass. Top with 3 ounces club soda and 1 tablespoon simple syrup; gently mix. Top with a scoop (a heaping 1/3 cup) of best-quality vanilla ice cream, garnish with a few more cacao nibs, add a straw and serve immediately.
Nutrition information per serving:
Calories290Fat18 gSodium70 mg