Preparation Prepare a large bowl of ice and cold water. Trim asparagus to 5 inches long, then steam in a steamer over boiling water until crisp-tender, about 4 minutes. Transfer to cold water to stop cooking. Drain and pat dry. Season with salt. Stir oil into butter until incorporated. Cut prosciutto slices into roughly 3- by 3-inch pieces, then thinly coat with truffle butter and place an asparagus stalk at one edge. Roll up, leaving tip and end visible. Repeat with remaining asparagus and prosciutto.
Preparation Prepare a large bowl of ice and cold water. Trim asparagus to 5 inches long, then steam in a steamer over boiling water until crisp-tender, about 4 minutes. Transfer to cold water to stop cooking. Drain and pat dry. Season with salt. Stir oil into butter until incorporated. Cut prosciutto slices into roughly 3- by 3-inch pieces, then thinly coat with truffle butter and place an asparagus stalk at one edge. Roll up, leaving tip and end visible. Repeat with remaining asparagus and prosciutto.