Step 4: Make Chocolate Glaze
For the glaze, in a small saucepan, bring sugar, margarine, milk, and cocoa to a boil. Stir frequently; then reduce heat to a simmer for 2 minutes, stirring constantly. It'll look gloppy, but it's just the bubbles! Remove from heat and stir for another 5 minutes.
Add vanilla, stir, and immediately pour onto cake. Glaze dries really quickly, so spread it immediately and add any sprinkles now. Let this cool for an 1 hour, if you can wait that long!