Using a potato peeler slice the zucchini lenghtwise into strips.
Cut the leek into very fine julienne strips and cut the asparagus into 2 in even lenghts.
Cut out 4 sheets of parchament paper. 12 X 15 inch size. Fold in half. Draw a large curve to make a heart shape when unfolded. Cut along inside of line and open out.
Divide the vegetables between each heart. Position the filling on one side of the fold line and top with tarragon and the unpeeled garlic clove. Season to taste.
Brush the edges with the egg and fold over. You may also fold without using the egg. This takes a bit more practice. http://www.sundaysupper.com/parch.htm give directions and shows photos of the no egg technique. For Vegan, omit the egg. If you do want to seal it, use the cornstarch and water paste method.
Pleat the edges so it is sealed. lay on cookie sheet and bake for 10 minutes. Serve immediately.