Preheat oven to 425°
Mix well in one bowl, the egg yolks, yogurt, sour cream, lemon zest, pudding, cornstarch (I used a mixer but you can use a whisk.) Mix until all ingredients are combined and not lumpy. Set aside.
Add the sugar to the other bowl of egg whites and mix on high speed for 4 minutes until soft peaks form. Don’t over mix.
Transfer 2 cups of egg whites into the pumpkin mixture and fold it in using big folding motions. Now transfer the pumpkin mixture into the egg whites bowl and fold until smooth mixture forms and you don’t see egg whites.
Use a round 9” cake pan, line the bottom with parchment paper, and create parchment paper ‘wall’ that is 2” higher than the cake wall. We do that because the cake will rise in the oven higher than the cake pan and we want to prevent a spill. Spray with cooking spray all over.
Take a large foil square and cover the cake pan bottom. We do this because we will place the cake in a shallow water bath in the oven and we don’t want the water to penetrate the pan.
Transfer the batter to the round cake pan.
Place a large and shallow roasting pan in the hot oven and add two cups hot water to create a bath for the cake.
Place the cake in the ‘bath’ and bake for 15 minutes. Turn down the heat to 325° and bake for 1 hour.
Take the cake out and let it cool.
Refrigerate overnight.
Run a knife around the cake to separate it from the cake pan, place a large plate over it and flip the cake onto the plate. Take another large serving plate and do it again so the baked side of the cake is facing up. Sprinkle powder sugar and serve.
