Put lentils in a large plastic container with a wide-mouth top and pour in 3 cups cold water. Stir to ensure an even soak. Cover with a double layer of cheesecloth and secure with a rubber band around the rim. Soak at room temperature 12 hours.
Invert container and let water drain; then let drained beans stand in pitcher at room temperature 8 hours.
Rinse beans with cold water 3 times a day until all have sprouted (grown threadlike shoots), 2 or 3 days. (Putting them under a heat lamp speeds up the sprouting.) Rinse one last time, dry quickly with clean kitchen towels, and chill, covered.
*Find beluga lentils at well-stocked grocery stores and online.
Make ahead: Up to 1 week, chilled.