For the cake: Preheat oven to 350. Beat the egg yolks until creamy and light yellow. Add the sugar and blend well. Add the water and vanilla. Sift the flour, baking powder and salt, and add it to mixture. Mix well until smooth. Beat the egg whites in a separate bowl, add cream of tartar and beat until stiff peaks form. Fold egg whites into batter just until well combined. Pour into and ungreased 17x11 jellyroll pan. Bake for 18-25 minutes or until light brown. Cool. Cut cake into cubes into a large bowl and fold mousse into cake. Pour into a serving dish and chill until cold or several days in fridge.
Serve each serving with a scoop of ice cream, strawberries, a drizzle of strawberry syrup and whipped cream. (If you like more mousse in the cake and extra sauce, you can either not add all the cake to the mousse or 1 1/4 times the sauce and mousse part.)