In a Dutch oven or large kettle, bring 8 cups water to a boil. Add pearl onions; boil until tender, 6-7 minutes. Drain and rinse in cold water; peel and set aside., In a saucepan, melt butter. Stir in the flour, salt and pepper until smooth. Gradually stir in broth and cream. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in the parsley, cheese and onions., Pour into an ungreased 1-1/2-qt. baking dish. Cover and refrigerate overnight. Remove from the refrigerator 30 minutes before baking. Cover and bake at 350° for 15 minutes; stir. Top with pimientos if desired. Bake, uncovered, 10 minutes longer or until bubbly and heated through.