Step 1Rinse salmon. Place in large skillet, cover with cold water and add a heaping tablespoon of salt. Bring water to boil then turn off heat and let stand 25 minutes. Remove skin from salmon and refrigerate, covered, at least 1 hour.
Step 2Close to serving, scrub potatoes, cut in half lengthwise and steam over boiling water until tender when pierced with a knife, 25 to 35 minutes.
Step 3To serve, flake salmon onto 4 plates, add potatoes and intersperse with clumps of watercress. Spoon a little sauce over salmon and potatoes and garnish with chives. Serve remaining sauce on side.
Step 1Puree tofu in food processor or blender with yogurt, sour cream and oil until smooth. Scrape down sides; add lemon zest, juice, dill and garlic and process again until smooth and pale green.
Step 2Scrape into bowl and stir in all but a few chives. Taste for salt and season with pepper. Wipe bowl so that it looks neat, sprinkle remaining chives and chive blossoms, if using, over top. Cover and chill at least 1 hour. Makes about 1 cup.