Lightly toasted bread. Generous slathering of butter or margarine. Then, if you're a noobie, a very thin spread (but if you're an Aussie, an extremely thick spread) of Vegemite.
To me it tastes very similar to the burnt bits stuck to the pan after cooking a burger
It's not exactly the same thing, but it basically is that. It's the bits stuck at the bottom of a fermentation vat at a brewery.