We adapted this technique from chef Jean-Georges Vongerichten's version. Make the powdered orange zest (Steps one and two) several days ahead, and keep it in an airtight container in a cool, dry place; grind before using.
Heat oven to 275 degrees. line a baking pan with aluminum foil. Using a vegetable peeler, remove zest in large strips from 2 oranges. Place zest in small nonreactive saucepan; add sugar and 1 cup water. Set over high heat; bring to a boil. Reduce to a simmer; cook until liquid is syrupy, about 35 minutes.
Transfer zest to the prepared baking pan, and place in oven. Bake until zest is dry but not brown, 25 to 30 minutes. If zest begins to brown, reduce oven temperature to 250 degrees. Remove pan from oven, and let zest cool completely. Transfer zest to a spice grinder, and grind to a powder. Set the powder aside.
Using a paring knife, remove pith and outer membranes from the zested oranges. Carefully cut each segment away from membranes, and set segments aside.
Peel parsnips, and cut into 1-inch chunks. Place in a large saucepan; cover with cold water. Bring to a boil over medium-high heat. Reduce heat to a simmer, and cook until parsnips are very soft, 8 to 10 minutes. Drain in a colander. Return parsnips to pan.
Add 1/2 cup orange juice to parsnips, and season with salt and pepper. Return the saucepan to medium heat. Cook, mashing parsnips with the back of a wooden spoon or a potato masher, until orange juice has been incorporated and parsnip puree is hot, about 5 minutes; set aside in a warm place.
Sprinkle both sides of fillets with salt and pepper. Sprinkle 1 teaspoon powdered orange zest on top of each fillet. Heat a large saute pan over medium heat. Place salmon in pan, orange-zest-side up, and cover. Cook until salmon turns opaque three-quarters of the way through, about 5 minutes. Turn fillets over, and cook until orange crust is golden brown, about 2 minutes more. Remove salmon from pan; set aside in a warm place.
Pour the remaining cup orange juice into the saute pan. Using a wooden spoon, scrape up any brown bits from bottom of pan. Increase the heat to high, and cook until the sauce has been reduced by half and is slightly thickened, about 4 minutes.
Divide parsnip puree among four plates, and top with salmon. Spoon sauce and reserved orange segments over salmon; serve.