Preheat oven to 350ºF. Grease a 9-inch springform pan with oil, then line bottom with parchment paper. Lightly oil parchment paper. Finely grate enough lemon zest to yield 1 1/2 tsps then whisk into flour. Halve lemon, squeeze out juice and reserve 1 1/2 tbsps. In a large bowl, beat together egg yolks and 1/2 cup sugar with an electric mixer on high speed until pale yellow and thick, about 3 minutes. Reduce to medium speed and add 3/4 cup olive oil and reserved lemon juice, beating until just combined (mixture may appear separated). Using a wooden spoon, stir in flour mixture until just combined (do not beat). In another large bowl, with clean beaters, beat 4 egg whites and salt on medium-high speed until foamy. Add 1/4 cup sugar, a little at a time and continue to beat until egg whites form soft peaks, about 3 minutes. Gently fold 1/3 of whites into yolk mixture, and then fold in remaining whites, gently, but thoroughly. Transfer batter to prepared springform pan and gently rap on work surface to release bubbles. Sprinkle evenly with remaining sugar. Bake in center of oven about 45 minutes, until puffed and golden and a wooden pick inserted in center comes out clean. Cool cake in pan on rack 10 minutes, then run a knife around edge and remove sides. Cool cake to room temperature, remove bottom of pan and parchment. Transfer to a serving plate.