-
1
Preheat the oven to 350F (175C).
-
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
Line the bottom with a piece of parchment paper.
-
4
Into a small bowl, sift together the flour, baking powder, and salt.
-
5
In a stand mixer fitted with the whip attachment, whisk together the egg yolks and water on high speed for 1 minute.
-
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
Set aside.
-
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
Using one hand, gradually sift the flour mixture over the beaten yolks, and using a whisk with the other hand, fold it in.
-
10
(Setting the bowl on a damp towel will help steady it while you sift and fold.)
-
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
Pour the batter into the prepared baking sheet or springform pan and quickly spread it in an even layer.
-
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
Let cool in the pan.
-
15
Run a knife around the sides of the cake to loosen it from the pan.
-
16
Invert the cake onto a cutting board or large plate.
-
17
The cake will keep at room temperature for 3 days, or in the freezer for 1 month.
-
18
You can add the grated zest of 1 lemon or orange to the batter along with the egg whites.
-
19
Instead of the vanilla extract, you can use 1/2 teaspoon almond extract.
-
20
Sponge cake is easier to slice if made a day in advance.
