Combine flour and sugar; cut in butter until crumbly. Press into a greased 13x9-in. baking dish. Bake at 350° for 10-15 minutes or until lightly browned. Cool.
In a bowl, beat egg yolks; add the sugar, flour and salt. Stir in the rhubarb, cream and orange zest; pour over crust. Bake at 350° for 50-60 minutes or until a knife inserted in the center comes out clean.
In a large bowl, beat the egg whites, vanilla and salt on medium speed until soft peaks form. Gradually beat in the sugar, 1 tablespoon at a time, until stiff peaks form. Immediately spread over hot filling, sealing edges; sprinkle with nuts. Bake 12-15 minutes longer or until lightly browned. Cool for at least 1 hour before serving. Refrigerate leftovers.