Sponge Cake

Directions

1. 1
   Preheat the oven to 350F (175C).
2. 2
   Lightly butter just the bottom of a 12 by 18-inch (30 by 46-cm) rimmed baking sheet or 9-inch (23-cm) springform pan with sides at least 2 inches (5 cm) high.
3. 3
   Line the bottom with a piece of parchment paper.
4. 4
   Into a small bowl, sift together the flour, baking powder, and salt.
5. 5
   In a stand mixer fitted with the whip attachment, whisk together the egg yolks and water on high speed for 1 minute.
6. 6
   Decrease the speed to medium, add the sugar and vanilla, then increase the speed to high and continue to whisk until the mixture forms a ribbon when the whip is lifted, about 5 minutes.
7. 7
   Set aside.
8. 8
   In a clean, dry bowl and with a clean whip attachment, whisk the egg whites on high speed in the stand mixer until they form stiff peaks.
9. 9
   Using one hand, gradually sift the flour mixture over the beaten yolks, and using a whisk with the other hand, fold it in.
10. 10
    (Setting the bowl on a damp towel will help steady it while you sift and fold.)
11. 11
    When the flour is completely incorporated, use a rubber spatula to fold in one-third of the whipped egg whites to lighten the batter, then fold in the remaining whites.
12. 12
    Pour the batter into the prepared baking sheet or springform pan and quickly spread it in an even layer.
13. 13
    Bake until the cake is browned and the center springs back when gently pressed with a finger, 15 to 18 minutes in a baking sheet or 40 to 45 minutes in a cake pan.
14. 14
    Let cool in the pan.
15. 15
    Run a knife around the sides of the cake to loosen it from the pan.
16. 16
    Invert the cake onto a cutting board or large plate.
17. 17
    The cake will keep at room temperature for 3 days, or in the freezer for 1 month.
18. 18
    You can add the grated zest of 1 lemon or orange to the batter along with the egg whites.
19. 19
    Instead of the vanilla extract, you can use 1/2 teaspoon almond extract.
20. 20
    Sponge cake is easier to slice if made a day in advance.