Step 1

Arrange a rack in center of oven; preheat to 325°. Cut a 9" circle of parchment to cover bottom of springform pan. Grease pan with butter, dust with flour, and set parchment inside.

Step 2

Sift sugar, baking powder, salt, and remaining 2½ cups flour into a medium bowl. Stir in lemon zest.

Step 3

Whisk egg yolks and vanilla in a medium bowl. Add milk and whisk to combine, then add oil and whisk again to combine.

Step 4

Pour yolk mixture into dry ingredients. Fold batter with a wooden spoon, scraping bottom and sides of bowl, until creamy, glossy, and fully combined (about 6–7 folds).

Step 5

Using an electric mixer on medium-high speed, beat egg whites in a large bowl until soft peaks form. Add cream of tartar and continue to beat until stiff peaks form (do not overbeat; it will dry out the egg whites).

Step 6

Using a large spatula, fold one-third of egg whites into batter to lighten. Fold in remaining egg whites in two additions until batter is bubbly, shiny, and loose.

Step 7

Pour batter into prepared pan and bake cake until a tester inserted into the center comes out clean, 45–50 minutes.

Step 8

Run a very sharp knife between edge of cake and pan. Let cool in pan until cool to the touch, about 1 hour.

Step 9

Carefully remove adjustable body of springform pan and invert cake onto a platter. Peel off parchment. Serve plain or top with whipped cream or icing, if using.