In a large sauté pan, heat 3 tablespoons of the olive oil over low heat. Add the onions and sauté for 8 minutes. Add a few tablespoons water and continue to cook, stirring occasionally, until the onions are very soft, 8 to 10 minutes longer. Remove from the heat, transfer to a blender, and purée until smooth. You should have about 2 cups purée. Stir the truffle into the purée and keep warm.

In a large nonstick sauté pan, heat the remaining 3 tablespoons olive oil over high heat. Add the scallops and sauté, turning once, until golden on the outside and just opaque at the center, 4 to 6 minutes total.

Divide the onion purée evenly among warmed salad plates. Top with the scallops, again dividing evenly, and sprinkle with the fleur de sel and chives. Serve warm.

Variations:

If you cannot find spring onions (small, white bulbs on green stems), you can use 4 bunches green onions (scallions), white part only, and 1 yellow onion in their place.

In place of the truffle, trim the stem ends, wipe clean, and slice ¼ pound fresh porcini or chanterelle mushrooms, then sauté the mushrooms in olive oil until tender. Serve them with the scallops atop the onion purée.