Beat the egg white, sugar and cream of tartar at high speed till firm peak formed.
In a large mixing bowl, blend egg yolks, water, and oil until fully mixed. Then add flour, baking powder, and mix thoroughly.
Fold in the egg yolk mixture to the egg white mixture, and make sure the batter is well-mixed.
Pour batter into a 10” x 13” baking pan, bake at 356°F/180℃ for 15 minutes, and cool at room temperature.
Flip the cake over on a working surface, and press the cooling rack on the cake about a halfway deep to form a pattern on the cake.
Slice the cake into two equal parts horizontally.
Brush the cake surface with melted butter and coat it with another layer of egg yolk liquid.
Sprinkle the cake with some powdered sugar. Use a kitchen torch to caramelize sugar. Slice the cake in 4 equal parts to get 4 pieces of 2.5” x 6.5” cake slices.
Squeeze the piping bag of cream to create a small bun of 2” wide and repeat to form a quarter moon shape with 6 cream buns. Layer the cake slices on the sizes of the cream and keep the quarter moon shape. Full in the gap with fresh halved strawberries. Add another layer of cream on the strawberry. Top it with mixed berries of your choice.