Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper and set aside.
On a lightly floured surface, roll out the puff pastry to a 1/8-inch-thickness, or thin enough to cut out 8 (4-inch) circles. Using a 4-inch round cutter dipped in flour, cut out 8 circles. Place on the prepared sheet, cover with a second piece of parchment paper and place a second baking sheet on top. Bake until cooked through and light golden brown, about 25 minutes. Transfer to a wire rack to cool completely.
In a large saucepan, combine the water, wine, sliced onion, Meyer lemon slices, bay leaf, salt, and peppercorns. Bring to a boil and cook for 5 minutes, allowing the flavors to infuse. Add the scallops, lower the heat to a simmer, and cover the pan. Gently poach until firm and just cooked through, about 2 to 3 minutes. Drain on paper towels. When cool enough to handle, slice in half crosswise (or into thirds, if very thick). Place the scallop slices on a plate, cover, and refrigerate until ready to use.
Arrange 3 asparagus spears each in the center of 4 plates and drizzle each lightly with truffle vinaigrette. Place one puff pastry round on each asparagus stack and arrange a circle of alternating scallop and truffle slices onto each round. Spoon Truffle Vinaigrette lightly over the scallops and truffles. Repeat with the remaining ingredients, ending with a scallops and truffles on top, topped by a spoonful of the Lemon Creme Fraiche. Spoon the remaining creme fraiche around the edges of the plates and arrange a small bundle of mushrooms on the side of each plate. Garnish each plate with chopped chives and serve.
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