180g / 1 1/4 cup dry macaroni (I used mini shells)*
Bring a medium saucepan filled with water to a boil. Add a large pinch of salt and the cauliflower. Once the mixture returns to a boil, drop heat to low and simmer for 30 minutes. Drain, then process or blend until smooth (I used a small food processor). Measure out 75 g / 1/4 cup of the cauliflower puree and set aside. Reserve the rest for another use.
Preheat a water bath to 176°F (see steps above for a stove top sous vide setup). Add Jack and Gruyère to a large ziplock bag with 500g / 2 1/8 cup cold water. Using the water displacement method outlined above, remove as much air as possible from the bag and seal.
Cook sous vide for 30 minutes, then set aside to cool at room temperature for 15 minutes. While the mixture is cooling, set a fine-mesh basket strainer over a large bowl (preferably with a pour spout). Line the strainer with a paper towel (or cheese cloth). Once cooled, pour cheese water through the lined strainer. Measure out 500g / 2 1/8 cup cheese water. Reserve remainder for another use.
Bring cheese water to a boil in a medium saucepan over medium-high heat. Add sugar, stirring to dissolve. Add macaroni and cook until al dente (soft on the outside with some bite left on the inside). The macaroni will absorb most of the cheese water (9 - 10 minutes). Stir in cauliflower puree and season to taste with salt (I added just the smallest pinch).
* Want to bump up the health factor of this recipe? Try using whole wheat pasta.
Recipe by Kitchen Konfidence at http://www.kitchenkonfidence.com/2013/01/fat-free-mac-and-cheese-well-virtually-fat-free