So glad you like this idea! And I'm laughing at your choice Patricia
This is one of my favorite photos to take because, well, you need cake! Chocolate preferably!!
The trick here is to have a wide enough aperture to let enough light in to illuminate your subject without blowing out the other details.
I shot this at an ISO of 800, with an aperture of f/2.0. I shot in Aperture Priority as I was moving at the speed of a 4 year old. I expose for the cake and candles (thus their crisp look), pressing the shutter half way down, recompose and shoot. I shoot several shots one after another just to be sure I get the shot with a good expression. With him directly behind the candles I get a little more light on his face but you can also get a similar effect from the side. The more candles on the cake the smaller aperture you can use (the larger number).
ETA - It definitely helps to have all of the other lights off in the room!