Bring a large pot of water and 2 teaspoons of salt to a boil. Meanwhile, rinse the asparagus. Using both hands, snap off and discard the tough bottom ends of the asparagus spears. (They will naturally break at the right spot.) Cut each spear into 1-inch pieces. Fill a large bowl with lots of ice and water and set aside.
Make the vinaigrette: Prep the shallot, capers and parsley, and add them to a small bowl with the vinegar. Whisk in the olive oil until emulsified. Add salt and pepper to taste.
When the water boils, add the asparagus. Simmer until they’re bright green and tender, 3-5 minutes. Drain and immediately immerse them in the ice water to stop the cooking. When they’re cold, dry them well with a kitchen towel and refrigerate until ready to serve.
To serve, drizzle the asparagus with the vinaigrette.