Lemon zest and juice add sunny flavor to this moist olive-oil cake. A slice is lovely as is, but a topping of fresh berries and whipped mascarpone cream really makes it sing.
Cake: Preheat oven to 350 degrees. Brush a 9-inch springform pan with oil and line bottom with a parchment round; brush parchment.
Whisk together flour, baking powder, salt, and lemon zest to thoroughly combine. In the bowl of a mixer fitted with the whisk attachment, beat egg whites over medium-low until foamy. Increase speed to medium-high; slowly add 1/3 cup granulated sugar, beating just until whites hold soft peaks, 3 to 4 minutes. In another large bowl, beat egg yolks with remaining 3/4 cup granulated sugar on medium-high speed until thick, pale, and tripled in volume, 2 to 3 minutes. Slowly beat in oil, then lemon juice to combine (mixture may appear curdled). Stir in flour mixture just to combine. Gently stir one-third of egg-white mixture into yolk mixture to lighten. Then gently fold in remaining egg-white mixture until no streaks of white remain (do not overmix). Transfer batter to prepared pan; gently smooth top with a spatula.
Bake until cake is golden brown on top and springs back when lightly pressed, 45 to 55 minutes. Transfer to a wire rack; let cool 15 minutes. Run a knife between sides of cake and pan to loosen. Remove sides of pan; let cool completely.
Berries and Cream: Meanwhile, stir together berries, 2 tablespoons granulated sugar, and lemon juice in a bowl. Let stand at least 30 minutes and up to 2 hours. In another bowl, whisk cream until thick and silky but not holding peaks. Add mascarpone and remaining 2 tablespoons granulated sugar. Whisk just until soft peaks form.
Dust top of cake generously with confectioners' sugar. Serve with macerated berries and whipped mascarpone cream. Cake can be made ahead and stored in an airtight container at room temperature up to 2 days.