Heat oven to 350°F. Grease bottom and sides of a 8-inch round cake pan with nonstick cooking spray; line bottom with parchment paper and then spray parchment paper with nonstick cooking spray as well. .
In a large bowl, whisk together all-purpose flour, whole wheat flour, baking powder and salt until combined. In another bowl, whisk together yogurt, 1 cup of the sugar, eggs, clementine zest, vanilla extract and the caviar from inside the vanilla bean (save the scraped out pod!).
Put vanilla bean pod in a small bowl and cover with remaining 1/3 cup of sugar. Set aside.
Slowly stir wet ingredients into dry ingredients until combined. Do not overmix. Stir in oil. Pour batter into prepared pan.
Bake 40 to 50 minutes until a toothpick or knife inserted in the center comes out clean. Cool about 10 minutes in pan, then remove from cake pan and transfer to a cooling rack with a rimmed baking sheet underneath it.
While the cake is cooking, heat a small saucepan over medium heat and cook the clementine juice, sugar/vanilla bean pod mixture, stirring until sugar is dissolved. Let vanilla bean pod stay in this mixture until the cake is on the cooling rack. Then remove the vanilla bean pod and pour the juice/sugar mixture evenly over warm cake on cooling rack. Cool completely.
If desired, sprinkle top with powdered sugar before serving.