Sugar melts at about 320°F and will turn to a clear liquid at that temperature. As the heat increases, the liquid sugar will turn golden brown. Toward 350°F it will darken. When the liquid cools it turns to a crisp glaze.
This can be done under the broiler but I have tested my Crème Brulee recipe with the broiler technique and the custard heats up a little too much for my taste. Using a blowtorch lets you melt the sugar quickly while the custard remains cool. This will set you back about 30 bucks for a blowtorch available in most kitchen stores. Not bad for a bit of heaven!