To make a green-onion brush, place the tip of a knife at the onion's middle and slit through the green ends. Place the onion in ice water, which will cause the "leaves" to curl; keep the green-onion brush in water until ready to use.
Assemble the wreath on a cookie sheet. Cover loosely with plastic wrap and refrigerate for up to two hours. Bake as directed in the recipe.
Place the baked wreath on a large decorative platter (pound at your favorite party good store) and surround it with rosemary sprigs.