In the upcoming MAKE, Vol 25, we have an article by Scott Heimendinger that shows you how to make a sous vide immersion cooker. What is it? It's a machine to slow-cook food (sealed in a plastic bag) in a water bath at a precise temperature.
We've put the complete article up at Make Projects.
From the intro:
Most sous vide (soo-veed) cooking machines are commercial models that cost north of $2,000, and the first "home" version, the countertop SousVide Supreme, is priced in the neighborhood of $450 (not including vacuum sealer), which is still a steep investment for something that essentially keeps water warm. I decided to build a better device on the cheap. Behold, the $75 DIY Sous Vide Heating Immersion Circulator! By scrapping together parts from eBay and Amazon, I created a portable device that heats and circulates water while maintaining a temperature accurate within 0.1°C. And unlike the SousVide Supreme, it mounts easily onto larger containers, up to about 15 gallons, for greater cooking capacity. The water is heated by three small immersion heaters and circulated by an aquarium pump to keep the temperature uniform. An industrial process temperature module controls the heaters, and an eye bolt lets you clamp the entire apparatus to the rim of a plastic tub or other container. To cook sous vide, you also need a vacuum sealer, which this project does not include. I bought a good one new for about $112.
From the "Kitchen Tests" section:
To reveal the power of sous vide, cook an egg in the shell (no plastic needed) at 64.5°C for 1 hour. This yields an amazing transformation: perfectly soft whites, not runny or rubbery, and a yolk with the consistency of a rich pudding. It's impossible to achieve this through any other cooking method, and it's spectacular the first time you experience it.
I expanded on this amazing transformation by breading the yolks and quickly deep-frying them to add a crunchy shell. See my recipe here.