Chiffon Cake

2¼ cups (315 g) all-purpose flour
2 tsp. baking powder
1½ cups (300 g) sugar
¾ tsp. salt
½ cup vegetable oil, such as safflower or sunflower
6 large egg yolks
¾ cup water
2 tsp. vanilla extract
1½ tsp. lemon zest, grated
10 large egg whites
¼ tsp. cream of tartar or lemon juice

Preheat the oven to 325°F. Line the bottom of a 10" springform pan with 3" sides with parchment paper cut to fit exactly. Do not grease the sides of the pan.
Sift together the flour and baking powder into a large mixing bowl. Add 1¼ cups of the sugar and the salt and whisk to combine. In a small bowl, whisk together the oil, egg yolks, water, vanilla, and lemon zest. Make a well in the flour, add the yolk mixture, and then whisk thoroughly and quickly for about 1 minute until very smooth.
Place the egg whites in a large mixing bowl. Using a mixer fitted with the whisk attachment, beat on medium speed until frothy. Add the cream of tartar or lemon juice and beat on medium-high speed until the whites hold soft peaks. Slowly add the remaining ¼ cup sugar and beat on medium-high speed until the whites hold firm, shiny peaks. Using a rubber spatula, scoop about one third of the whites onto the yolk mixture and fold in gently to lighten the batter. Gently fold in the remaining whites just until combined.
Pour the batter into the prepared pan, smoothing the top with an offset spatula if necessary. Bake until a cake tester inserted into the center comes out clean, 45–55 minutes. Let cool in the pan (the sides of the pan will help hold the structure of the cake as it cools) on a wire rack. To unmold, run a small, thin knife around the sides of the pan to loosen the cake and then release and lift off the pan sides. Invert the cake, peel off the parchment, and then use as directed in individual recipes. The cake will keep, well wrapped, in the refrigerator for up to 4 days or in the freezer for up to 1 month.