Preheat the oven to 350 F (177 C). Grease and line the bottom of a 9- inch (23 cm) springform or cake pan with parchment paper.
In a large bowl, whisk together the flour, baking powder and salt together until well combined.
2 cups (240 g) all purpose flour, 2 teaspoons baking powder, ½ teaspoon salt
In a large mixing bowl fitted with whisk attachment, whisk the sugar and lemon zest together until they are the consistency of wet sand. On low, whisk the eggs and lemon sugar together until all the eggs are combined. Increase the speed to high and whip for 2 -3 minutes. The egg and sugar mixture will be thick and light yellow in color. 1¼ cups (250 g) granulated sugar, 2 large lemons, zested, 3 large eggs, room temperature
With the mixture on low speed, stream in the olive oil, followed by the limoncello, lemon juice and sour cream. Once all the ingredients are mixed in, mix together for another minute on low to fully combine. Scrape the sides and bottom of the mixing bowl as needed. On low, whisk in the dry ingredients. Mix until just incorporated. ¾ cup (180 ml) olive oil, ½ cup (120 ml) limoncello, ¼ cup (60 ml) lemon juice, ¼ cup (60 g) sour cream, room temperature
Evenly pour the limoncello and lemon cake batter into the prepared pan. Bake the Italian liqueur cake for 35 - 45 minutes or until a toothpick inserted into the center of the cake comes out clean or with a few moist crumbs. The crust will be golden brown and the top should bounce back when gently pressed.
Cool the cake in the pan for 15 minutes. Gently release the side of the springform pan, remove the ring and allow the cake to cool completely to room temperature before topping with frosting.
Place a mixing bowl and whisk attachment in the fridge or freezer for about 15 - 20 minutes before making the frosting recipe. On low, whisk the mascarpone cheese until smooth. Once smooth, mix in the vanilla extract and powdered sugar until well combined. Once all the sugar has been added, mix in the heavy cream slowly on low speed. Once all the heavy cream has been added, increase the mixer speed to medium for about 2 - 3 minutes or until the frosting is light and fluffy.
8 oz. mascarpone cheese, 1 cup (120 g) powdered sugar, 2 teaspoons vanilla extract, 1 cup (240 ml) cold heavy whipping cream
Once the cake is completely cooled, top the limoncello cake with the mascarpone frosting. Create decorative swirls using the back of a spoon. Drop dollops of lemon curd into the swirls. Using the back of a spoon, gently swirl the curd into the swirls of mascarpone frosting.
¼ - ½ cup lemon curd