Individual servings of Asparagus Mousse look particularly attractive when garnished. Reserve 4 cooked asparagus tips and set them aside at room temperature. Just before serving, place 1 asparagus tip on each mousse and lay a curl of lemon zest alongside.
1. Boil, steam, or bake the asparagus until tender. Drain and transfer to absorbent paper, reserving 4 tips for garnishing, if desired. Pat the stalks dry and cut into 1-inch lengths. Transfer to the container of a blender or processor and whirl until smooth. Add the egg yolks, one at a time, then blend in the tarragon, nutmeg, salt, and pepper. Pour into a large mixing bowl.
2. Preheat the oven to 350°. Generously butter 4 ramekins or individual souffie molds. In a separate bowl, whisk the egg whites until soft peaks form and fold into the asparagus purée. Pour into the prepared baking dishes and loosely cover each with aluminum foil. Arrange the baking dishes in a shallow pan, then pour in boiling water to the depth of 1 inch. Bake for 25 to 30 minutes or until the slender blade of a paring knife inserted in the center comes out clean. Garnish with asparagus tips and lemon zest curls and serve immediately.