Preheat oven to 325 degrees F. Spray a 9″ x 13″ baking sheet with non-stick cooking spray and line with parchment paper; set aside.

In a medium mixing bowl, whisk together the flour, baking powder, and salt; set aside.

Place the egg yolks and 5 ounces of sugar into the bowl of a stand mixer and whisk on high for 2 minutes, or until the mixture becomes pale yellow and ‘ribbons’ when lifted. Add the water, vegetable oil, and vanilla and whisk to combine. Add the dry ingredients and whisk just to combine. Transfer the batter to a mixing bowl while you whisk the egg whites.

Place the egg whites and cream of tartar into a clean bowl and whisk on high using the whisk attachment until it becomes foamy. Decrease the speed to low and gradually add the remaining ounce of sugar. Increase speed to high and continue whisking until stiff peaks form.

Transfer 1/3 of the egg whites to the batter and whisk until well combined. Add the remaining egg whites and fold gently.

Transfer the batter to the prepared baking pan and tilt pan to coat until batter is evenly distributed. Bake for 22 to 25 minutes, until a toothpick inserted in the center comes out clean. Remove from the oven to a cooling rack and allow to cool completely.

Place mixing bowl and whisk in the freezer for 15 to 20 minutes.

Place the vanilla extract, sugar, and cocoa powder in the cold bowl. Stir in about 2 tablespoons of the cream to form a thick paste.

Add the rest of the cream and beat until stiff peaks form.

Cut three 4″ squares out of the chiffon sheet cake.

Brush the cake layers with vodka and allow to soak in for 5 minutes.

Place one cake square on a serving plate. Top with whipped cream. Repeat layers until all cake is stacked and topped with whipped cream.

Cover sides of cake with whipped cream. Dust top with cocoa powder.