Step 1

Remove greens from ramps, and reserve for another use. Trim white root ends of ramps. Place trimmed ramps in a medium size heatproof bowl or a rimmed heatproof dish; set aside. Combine vinegar, 1/2 cup water, and sugar in a small saucepan; bring to a boil over medium-high. Cook, stirring constantly, until sugar has dissolved, about 30 seconds. Remove from heat; pour over ramps in bowl. Cover and refrigerate until ready to use.

Step 2

Fill a large bowl with ice water; set aside. Place 4 cups water and 1 tablespoon salt in a small saucepan; bring to a boil over high. Cut off tips from asparagus to yield about 11/2 cups tips; set asparagus stems aside. Add asparagus tips to boiling water. Cook until crisp tender, about 2 minutes. Drain. Transfer asparagus tips to ice water; let stand 5 minutes to stop cooking process. Drain again, and set aside. Set aside small saucepan.

Step 3

Thinly slice reserved asparagus stems to yield about 10 cups stems. Set aside. Melt butter in a Dutch oven or a wide pot over medium-high. Add sliced asparagus stems; cook, stirring occasionally, until tender and liquid from asparagus is almost evaporated, about 10 minutes. Add milk, cream, and mace; bring to a simmer over medium-high. Simmer, stirring occasionally, until asparagus has completely softened and liquid has reduced slightly, about 10 minutes. Remove from heat; remove and discard mace.

Step 4

Transfer mixture to a blender. Secure lid on blender, and remove center piece to allow steam to escape. Place a clean towel over opening. Process until completely smooth, about 45 seconds. Place a fine wire-mesh strainer over small saucepan. Pour some of the asparagus mixture into strainer (about 2 cups, depending on size of your strainer), stirring to strain asparagus soup into saucepan. Discard strained solids, and rinse strainer well. Repeat straining process until all soup has been strained. Add ramp vinegar, white soy sauce, and remaining 1 teaspoon salt; stir to combine.

Step 5

Cut pickled ramps in half lengthwise, and chop crosswise into about 1/4- to 1/2- inch pieces. Ladle soup evenly into 6 bowls (about 1 cup each). Sprinkle bowls evenly with chopped hazelnuts and asparagus tips. Garnish with desired amount of chopped pickled ramps; reserve remaining pickled ramps for another use. Drizzle soup evenly with hazelnut oil. Serve immediately.