The slotted spoon is used in modernist cooking primarily when doing spherification. Whether making small spheres such as caviar or large spheres, often made using reverse spherification, you will need to remove the spheres from a liquid. A slotted spoon is the ideal tool for doing this.
Although they are referred to as "slotted spoons," the spoons actually have small holes in them to allow the setting liquid to run out leaving the spheres in the spoon.
Many of the molecular gastronomy kits come with a slotted spoon. Also kitchen supply stores often carry them.
The best slotted spoon we've seen is sold by Modernist Pantry, which they call a Stainless Steel Caviar Strainer. The bowl of the spoon is nice and deep and the holes are the ideal size for this application. This spoon is also inexpensive coming in at around $5.00.
The All-Clad Slotted Spoon (above) is a high-quality spoon that should be useful in your kitchen for numerous functions. It's made of polished, nonreactive 18/10 stainless steel and is dishwasher safe. It also has a comfortable ergonomic handle for ease of use.
If you're really into making large quantities of caviar using a Rapid Caviar Maker you will probably want a larger slotted spoon. There are a couple options, the first is a skimmer normally used for removing particles from the surface of a liquid. The best ones for spherification are the ones with small holes and a deeper bowl. This Chef Skimmer with Soft Grip Handle is made of stainless steel with a non-slip grip. It has 4 inch (10 cm) diameter and is 14 inches (36 cm) long.If you want to take the slotted spoon to a higher you level can use a scoop colander to retrieve large numbers of spheres. An example of this is the OXO Good Grips Large Scoop Colander, Stainless. It's made of stainless steel and has a soft, comfortable, non-slip handle.