Depends on what you want from caramalising really? If your just after some nice caramel tones pull out 2-4L(depending on batch size) and boil it hard to reduce to a syrup. Add it back to the kettle 20 mins before end of boil.
If your after toffee notes-good in some beers, awfull in others. Draw off a quarter of your wort before the boil starts(before you've added hops). Boil this hard and reduce to a very thick sticky syrup and leave. Add a few pints of your wort 15 mins from the end of the boil to the sticky stuff, swirl around to make a thick gravy and pour this into the kettle. You can top up the wort with boiling water but make sure your wort boils for at least 10 mins before the end of the boil.
I've tried both methods and it is a bit hit and miss all depending on what wort you have to reduce. Works well on strong ales and especially well if you mash at a high temp and have a sweet wort to start with. Particularly good for winter warmer style beers. Might work in stouts but I don't brew many stouts(none).
Hope this helps a bit. :thumb: