Grease two 8-inch cake tins and line the bases with parchment paper. Preheat oven to 350°.
In a stand mixer fitted with a whisk, beat sugar, eggs, salt and vanilla until pale and fluffy. In a separate bowl, combine olive oil, milk, lemon juice and zest, then slowly stream into the egg mixture. Sift the flour and baking powder into the mixer bowl, then fold together by hand.
Divide batter between the two tins and bake for 30 minutes, or until the top feels springy and a wooden skewer comes out clean. Invert onto cooling racks and cool to room temperature.
Increase oven to 430°F.
To make the meringue, add egg whites to a clean stand mixer bowl. On medium speed, whisk to soft peaks, then begin adding the sugar one spoon at a time. Once all the sugar is incorporated, continue beating until the meringue is stiff, glossy and all the sugar has dissolved. Transfer to a piping bag fitted with a star nozzle.
Place one cake on an oven-proof serving plate. Spread the marmalade evenly across the surface, followed by a ½ inch layer of meringue. Place the second cake on top.
Pipe lines of meringue up the sides of the cake. Pipe rosettes on top. Place into the preheated oven until the meringue is burnished all over, watching closely to avoid burning, about 2 minutes. Serve immediately.