There are a few different ways that you can thicken your creme brulee. One way is to cook it for a longer period of time. This will allow the water to evaporate out of the custard, leaving it thicker. Another way is to add a thickener such as cornstarch, flour, or gelatin. These need to be added before cooking the custard. Whisk them in until they are fully dissolved. Finally, you can add some heavy cream to the custard. This will make it richer and thicker. Just be careful not to add too much or it will be too sweet.