Vietnamese Flan Cake

1.Heat 3/4 cup sugar in a saucepan over medium heat until dark golden. Immediately pour caramel into a 9-inch cake pan and swirl around the bottom and up the sides a bit.
2.In a large bowl add 6 eggs and condensed milk. Whisk until everything is well combined. Add 4 cups milk, 6 tablespoons sugar and 2 teaspoons vanilla and whisk until combined. Set aside.
3.Separate 3 eggs from yolks to whites. In a medium bowl using an electric beater, beat egg yolks, 1/3 cup milk (30 grams), 1 teaspoon vanilla, and oil. Sift the flour into the mixture and mix well.
4.Preheat oven to 325 degrees. With a hand mixer, beat egg whites in a large bowl until foamy and opaque. Add 1/4 cup sugar (50 grams) and continue to beat until stiff peaks form. Carefully fold egg whites into egg yolk mixture.
5.Strain custard through a sieve into the prepared cake pan. Spoon cake batter on top of custard. Bake for about 30-40 minutes, until jiggly but set. If the cake browns too quickly, cover with aluminum foil while you continue to bake.
6.Let cool completely, then refrigerate for at least 8 hours or overnight. To remove the flan, first let the pan sit in hot tap water for about 1 minute. Run a knife around the circumference of the cake. Place a serving plate over the cake pan, and turn the entire flan over onto the plate. Tap the pan and it should release the cake. Serve immediately.