Almost all wedding photographers photograph the cutting of the cake, but many do not take a picture of the cake itself before the cutting begins. How this is best done depends to a large extent on the available light and the location of the cake. Find the best background available, and decide whether there is sufficient ambient light to manage without flash. If so, this may be the best way to photograph the cake. If ambient light is insufficient, the best approach is probably to bounce a flash off a a white ceiling or a reflector held by an assistant over the cake - carefully! Don't forget to go in close to capture some of the colour and detail, and try a couple of shots with the camera at an angle of about thirty degrees to the vertical. Take care with the exposure because white icing can be very reflective and detail is easily lost in the highlights. One rewarding approach is to use a mirror to get a second, reflected image of the cake in the one picture. However, a relatively large mirror is required. Suitable circumstances are rarely available.
When photographing a wedding cake, take careful note of the prevailing colour temperature. Light from numerous sources is likely to be present. There may be natural light mixed with tungsten, fluorescent or other sources. There may also be coloured walls or ceilings reflecting light into an already complex mixture. Take a couple of shots to find the best colour temperature setting before working on the final image. Although colour temperature errors are visible in any image, even the least trained eyes will spot them in an image of a white wedding cake.