Created by KittenCal on March 4, 2013
Step 1: In a heavy-bottomed small saucepan, stir together sugar, cocoa powder and cornstarch.
Step 2: Add milk and cook, stirring over medium-low heat until thickened and bubbly. Cook and stir for 2 minutes more.
Step 3: Remove from heat, then stir in vanilla.
Step 4: Serve the sauce warm or cool.