Ingredients

• 1/2 medium onion, chopped
• 1 small carrot, peeled, chopped
• 1/2 cup dry white wine
• 1 pound mussels, debearded, scrubbed
• 2 bunches asparagus (about 1 1/2 pounds), trimmed, stalks peeled
• Kosher salt
• 3/4 cup (1 1/2 sticks) chilled unsalted butter, cut into pieces
• 1 tablespoon Sherry vinegar
• 1 cup locust (acacia) flower (optional)

Instructions

1. Bring onion, carrot, and wine to a boil in a medium saucepan. Add mussels and return to a boil. Remove from heat, cover, and let sit 10 minutes.
2. Meanwhile, cook asparagus in a large pot of boiling salted water until bright green and crisp-tender, about 5 minutes. Using tongs, transfer to a bowl of ice water. Let cool, then drain and set aside. Reserve pot with water.
3. Strain mussel mixture through a sieve into another medium saucepan (you should have about 1/2 cup). Discard (or eat!) mussels and vegetables. Bring cooking liquid to a boil, reduce heat, and simmer until reduced to 1/4 cup.
4. Whisking constantly, add butter, a piece at a time, incorporating before adding the next piece. Whisk until sauce is emulsified. Whisk in vinegar; season with salt.
5. Just before serving, warm asparagus in reserved pot of hot water. Drain, pat dry, and transfer to a platter. Gently mix locust flowers, if using, into sauce and spoon over asparagus.