Preheat the oven to 400 degrees.
Fill a large pot with water, add 1 tablespoon salt, and bring to a boil. If the asparagus are thick, peel them halfway up the stalk with a vegetable peeler. Immerse the asparagus in the boiling water and cook for 2 minutes. Drain the asparagus and put them immediately into a large bowl of ice water to set the bright green color. Allow to chill for 2 to 3 minutes. Drain and pat the asparagus dry.
Gather 6 to 8 asparagus spears into a bundle with the tips together, and wrap a slice of prosciutto securely around the middle. Repeat to make 6 bundles. Brush a rectangular baking dish (large enough to hold the bundles in one layer) with 1½ tablespoons of olive oil. Place the bundles seam side down in the baking dish, arranged side by side, with the tips facing the same way. In a small saucepan, heat the truffle butter and 1½ tablespoons of olive oil until the butter melts. Drizzle it over the bundles. Sprinkle with ¾ teaspoon fleur de sel, ½ teaspoon pepper, and the Gruyère and bake for 12 to 15 minutes, until the butter is sizzling and the cheese melts and starts to brown. Serve hot.
Copyright 2014, Make It Ahead by Ina Garten, Clarkson Potter/Publishers, All Rights Reserved