Heat the oven to 350 degrees and grease a 9 x 13 pan with cooking spray.
In a small bowl, whisk together the flour, baking powder and salt. Set aside.
Using a stand mixer or hand mixer, beat the six egg yolks on high speed with ¾ cup sugar and vanilla extract until the mixture is pale yellow, thick and ribbons of egg yolk stream down when you lift the beater.
In another mixing bowl, beat the six egg whites on high speed with the remaining ¼ cup sugar and cream of tartar until soft peaks form.
Stir in the milk into the egg yolk mixture. Add half of the dry ingredients and stir until combined. Repeat with the second half of dry ingredients.
Gently fold in the egg whites. Continue to fold until you can no longer see any white.
Pour into greased pan and bake for 25-30 minutes. The cake is done when you insert a toothpick, and it comes out clean. Allow to cool.
While cooling, make the whipped topping by beating heavy cream and 1 tablespoon of sugar on high speed in a mixing bowl until soft peaks form.
Once cool, pierce the cake with a fork all over. Pour the spiced orange milk mixture all over the cake. Spread whipped topping on cake, cover and refrigerate for at least four hours to allow the cake to absorb the milk. This can also be done overnight. Cut into squares and serve. Enjoy!