1) Caramelize 1/2 cup sugar in 9" (about 3-1/2 to 4" inches deep) pan.Set Aside.For the Flan mixture,beat together first 5 ingredients with 1/2 cup sugar in a deep bowl.set aside.
2) To make Cake Batter, sift flour with 1/4 cup sugar,baking powder and salt. Place in small bowl and make well in the center. Place 2 egg yolks,oil,vanilla extract and orange juice in well. Stir until blended, starting from center.
3) Beat egg whites with cream of tartar until foamy. Gradually add remaining 1/4 cup sugar, beating until stiff but not dry. Gently fold batter into whites.
4) Pour Flan mixture into caramelized pan. Gently spoon batter over flan mixture. Place pan in larger pan and pour hot water into larger pan (Baine marie) until it reaches half depth of cake pan. Bake at 170 degree celsius for 50 to 60 minutes or until cake is done. Cool on a rack and chill until ready to serve. Invert onto serving platter.
Note: don't tap the pan so as the batter will not sink into the flan mixture.