The secret to traditional creamy mashed potatoes is simple -- butter and milk or cream, and lots of it. Such a treatment adds a lot of fat and calories, however, not to mention the fact that it makes mashed potatoes off-limits to the lactose intolerant and any vegan dinner guests. If you want to achieve that creamy texture but avoid all the dairy, you can, but you need to have a few tricks up your sleeve.
Pass potatoes through a potato ricer. A potato ricer is a specialty tool that creates a fine-grained mash by forcing the cooked potato through the fine holes of a mesh sieve. They look somewhat reminiscent of giant garlic presses and work on a similar principle.
Use olive oil. In place of butter, add olive oil to your cooked and mashed potatoes until you achieve the desired creamy consistency. Here, you are simply substituting a vegetable-based fat for an animal fat, so you won't save any calories this way.
Add chicken or vegetable stock. Use it in place of the milk in your favorite recipe, although you may find you need less stock, proportionally speaking. Alternatively, you can use a little of the water you used to boil the potatoes in place of the milk.