1. Preheat oven to 350°F. Lightly grease 9-inch round baking pan. Line bottom with wax paper circle; lightly grease wax paper.

2. Mix flour, cream of tartar, baking soda and salt in medium bowl. Beat butter, 1 cup of the sugar and vanilla in large bowl with electric mixer on high speed until light and fluffy. Add eggs and sour cream; beat on low speed until well blended. Gradually add flour mixture, beating on low speed until well mixed. Spread evenly in prepared pan.

3. Bake 45 to 50 minutes or until cake pulls away from sides of pan and toothpick inserted in center comes out clean. Cool in pan 10 minutes on wire rack. While cake is cooling in pan, mix orange juice, remaining 1/3 cup sugar and saffron in small saucepan. Bring to boil on medium heat, stirring constantly to dissolve sugar. Cover to keep warm.

4. Loosen cake from sides of pan with small knife or metal spatula. Invert cake onto serving plate. Pierce holes in hot cake with metal or wooden skewer. Spoon warm syrup evenly over hot cake. Let stand until cake has cooled and syrup has been absorbed. Garnish with orange slices, orange peel and/or whipped cream, if desired.