Divide half-and-half between two 8-ounce glasses. Stir 2 tablespoons seltzer water into each glass. Stir 2 tablespoons Cocoa Syrup into each glass. Serve immediately. Makes 2 servings.
In a small saucepan stir together sugar substitute, unsweetened cocoa powder, and salt. Gradually add boiling water, stirring until smooth. Bring to boiling over medium heat, stirring constantly. Reduce heat. Simmer, uncovered, about 2 minutes. Remove from heat. Stir in vanilla. Cool. Store in a tightly covered container in the refrigerator for up to 3 weeks. Makes about 1/2 cup.