Prepare the Egg Whites: In a large mixing bowl, beat the egg whites and cream of tartar with a hand mixer or whisk until stiff peaks form. Set aside.
Mix Dry Ingredients: In another bowl, combine the flour, sugar, and salt. Mix well and set aside.
Combine Wet Ingredients: In a third bowl, whisk the egg yolks, water, and vanilla extract. Stir this mixture into the dry ingredients until fully incorporated.
Fold in the Egg Whites: Gently fold the egg whites into the batter, being careful not to deflate the mixture. Fold until the batter is just combined and airy.
Bake: Pour the batter into a greased cake pan. Bake at 350°F (175°C) for 25–30 minutes, or until the cake is golden on top and a toothpick comes out clean.
Cool and Serve: Allow the cake to cool completely on a cooling rack. Once cooled, slice and serve with your favorite toppings, such as whipped cream, fresh fruit, or chocolate syrup.