Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   8      ounces        tuna -- #1 sushi-grade
                        salt -- to taste
                        freshly-ground black pepper -- to taste
   1      small         sweet potato -- peeled, and
                        -- chopped 1/4" cubes
   1      medium        cucumber -- sliced lengthwise
     1/4  medium        red onion -- finely chopped
   1      teaspoon      saffron
     1/2  cup           white wine vinegar
   2      tablespoons   dijon mustard
     1/2  cup           extra-virgin olive oil -- plus
   2      tablespoons   extra-virgin olive oil

Preparation:

Bring 6 quarts of water to a boil and add 2 tablespoons salt. Slice tuna into 4 equal pieces and place each between lightly-oiled pieces of aluminum foil. Lightly pat tuna with a cleaver until paper thin. Carefully flip each piece onto a chilled plate and refrigerate, wrapped in plastic. Place sweet potato cubes into boiling water and cook until tender yet firm (3 to 4 minutes). Rinse under running water until cool and set aside. Remove seeds from cucumber and cut into 1/8-inch thick half moons with skin on. Place onion, saffron and white wine vinegar to a boil and reduce by half. Place vinegar mixture in blender with mustard and blend until smooth. Drizzle in a half cup extra-virgin olive oil until emulsified and season with salt and pepper. Set aside. Remove tuna plates from refrigerator and season with salt and pepper. In a mixing bowl, dress cucumbers and sweet potatoes together with 2 tablespoons extra-virgin olive oil and season with salt and pepper. Divide sweet potato mixture in center of each plate, drizzle with saffron vinaigrette and serve immediately. Source: MOLTO MARIO with Mario Batali From the TV FOOD NETWORK - (Show # MB-5635)