Preheat the oven to 350°F. In an 8X8 square pan/dish, mix together flour, sugar, cocoa, baking soda, and salt with a fork, making sure it is really blended together. Add the water, vanilla, oil, and vinegar, and again, mix together so that it's really blended together. Use a spatula to scrape down the sides if necessary.

Place in oven and bake for about 30 minutes, or until a knife comes out clean. Cool on a rack completely (2 hours). Seriously, wait 2 hours, or it will collapse in the centre.

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!