In a heavy saucepan, combine cocoa powder, sugar and salt (if using). Grad
ually stir in boiling water. Stir frequently over medium heat until smooth
and slightly thickened, about 10 minutes. Remove from heat; stir in vanil
la extract.
Pour mixture into a 3-cup container with a tight fitting lid. Label with d
ate and contents. Store in refrigerator. Use within 10-12 weeks.
Makes about 2 2/3 cups Homemade Chocolate Syrup Mix.