Heat oven to 350 degrees F. Grease bottom and sides of a 9-inch round cake pan with baking spray with flour; line bottom with parchment paper and spray paper.

In a large bowl, whisk together flours, baking powder and salt until combined. In a separate large bowl, whisk together yogurt, 1 cup sugar, eggs, clementine zest and vanilla until combined.

Slowly stir wet ingredients into dry ingredients until just combined. Stir in oil. Pour batter into prepared pan.

Bake 40 to 50 minutes until a toothpick inserted in the center comes out clean. Cool 10 minutes in pan, then carefully remove from cake pan and transfer to a cooling rack with a rimmed baking sheet or clean sheet of parchment or wax paper underneath.

Meanwhile, cook the clementine juice and remaining 1/3 cup sugar in a saucepan over medium heat, stirring until sugar is dissolved. Carefully pour evenly over warm cake on cooling rack. Cool completely.

Sprinkle top with powdered sugar before serving, if desired.