InstructionsStep 1: Prepare the oven. Preheat it to 325 degrees. Lightly grease the bottom and sides of an 8 x 8-inch baking dish.Step 2: Whisk the egg whites until stiff peaks form, and keep them aside.Step 3: Mix the egg yolks with powdered sugar until pale yellow. Then, add the butter along with water. Beat constantly until evenly incorporated. Next, stir in the flour and cinnamon until well blended. Gradually whisk in the milk and vanilla extract.Step 4: About 1/3 at a time, fold in the egg whites.Step 5: Into the prepared pan, transfer the batter and place it in the preheated oven. Bake for about 40 to 60 minutes or until the center of the cake is barely jiggly. Tent the cake with aluminium foil if the top browns too quickly.Step 6: Slice and serve. Enjoy!