• Get ready. Preheat the oven to 350°F. Brush the bottom and sides of a 9-inch springform pan with olive oil. Line the bottom of the pan with parchment paper, brush the parchment with a thin layer of olive oil, and set aside.
• Beat the egg whites to stiff peaks. In a large mixing bowl with a hand mixer, whip the egg whites on medium-high speed until stiff peaks form, about 3 minutes. Set aside.
• Mix the wet ingredients. In a large mixing bowl, beat the egg yolks, sugar, and olive oil on medium speed until smooth. Add the milk, limoncello, and lemon zest and beat on low speed until combined.
• Add the dry ingredients. Add the flour, baking powder, and salt and mix on low speed just until combined.
• Fold in the egg whites. With a wide spatula, gently fold half of the beaten egg whites at a time into the batter. To preserve as much of the air as possible, fold gently, rotating the bowl a quarter turn after each fold. Mix until no streaks of egg white remain before adding the second half.
• Bake the cake. Pour the batter into the prepared pan. Bake for 48 to 53 minutes, or until a toothpick inserted into the center of the cake comes out clean.

For the Limoncello Syrup

• Make the Limoncello Syrup. While the cake is baking, combine the sugar, limoncello, and lemon juice in a small saucepan. Heat over medium heat, stirring, until the sugar has dissolved. Set aside.
• Cool and drizzle. Let the cake cool in the pan for 15 minutes. Then, carefully release it from the springform pan and set it onto a wire rack. Prick all over the top of the cake with a toothpick. Use a pastry brush to apply the limoncello syrup over the surface of the cake. You may not need all of the syrup. Let the cake continue to cool to room temperature.

For the Meringue

• Make sugar syrup for meringue. In a small saucepan, combine the sugar, water, and lemon juice. Bring to a boil over high heat. Do not stir. Cook until the syrup registers 240°F (116°C) on a candy or instant-read thermometer, 3 to 4 minutes.
• Beat the egg whites to soft peaks. Place the egg whites in a large heat-proof mixing bowl set on a damp tea towel or the bowl of a stand mixer fitted with the whisk attachment. The wet towel will prevent the bowl from sliding around on the counter while mixing. Beat the egg whites on medium-high speed until soft peaks form, 2 to 3 minutes.
• Make the Lemon Italian Meringue. With the mixer running, carefully and slowly pour the hot syrup into the egg whites. Aim for the side of the bowl to avoid the beaters. Continue beating until stiff peaks form and the meringue is cool, 4 to 5 minutes.
• Top the cake. Place the cake on a cake stand or serving dish. Use an offset spatula or a spoon to spread the meringue on top of the cake, leaving decorative swoops and swirls.
• Toast and serve. Lightly toast the meringue using a kitchen torch, or by placing it under a preheated broiler for 30 seconds. Slice and serve. The cake is best the day it is made.