Best lens for Newborn photography?

I have a Nikon D800. What would you say would be the best lens to use for newborn photography. Something that'll get me this look

Added (1). I have a 50 mm f/1.8, will that work well?

Probably the "nifty fifty", so you are well set up. Sorry, I could not open the link. The "look" of any photo is much more dependent on the skills of the photographer than on the lens in use. But certainly for a baby, or for any portrait closer than full-length adult you should not use a short lens, thus not 18mm or 28mm - 50 is good.

Whatever lens you have, you have to watch out with the D800. The pixel density is crazy, and the shot discipline demanded is considerable. Handholding is going to demand probably 2xFL or more if you want to get away with it, otherwise you're looking at a tripod.

PS If you have a D800 and have to ask a question like this, you're not experienced enough to be using a D800.

You have the camera and the lens to get that shot. However, you probably don't have the proper lighting to get that shot. I'm sure that was shot in a studio, with studio lighting.

A D800 is a seriously nice pro level camera, you have an amazing tool, you need to learn to use it now. Take some classes, learn about your camera and exposure. You should be able to look at that image and know exactly how to achieve those results. With your camera, lens and proper lighting It's not a hard shot to get, as long as the baby is asleep:-)