• Preheat oven to 325°F (170°C).

Using an Ankarsrum Mixer:

• Assemble Ankarsrum mixer with stainless steel bowl. Add granulated sugar and lemon zest. Whisk by hand until fragrant. Place dough knife in smaller hole, and position dough roller just off side of bowl. Add butter; slowly increase mixer speed to medium-high (6 o’clock), and beat until creamy, about 1 minute, using scraper to help move butter mixture around. (Mixture might stick to the roller in the beginning.) Add eggs, beating until just combined. Beat in vanilla.
• Lightly spray a 10-cup fluted tube pan with baking spray with flour.
• In a medium bowl, whisk together flour, baking powder, and salt. With mixer on medium-low speed (2 o’clock), gradually add flour mixture to butter mixture alternately with mascarpone and lemon juice, beginning and ending with flour mixture, beating just until combined after each addition and stopping as needed to scrape roller. Spread batter into prepared pan. Firmly tap pan on a kitchen towel-lined counter to settle batter.
• Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers 205°F (96°C), 1 hour to 1 hour and 5 minutes.
• Meanwhile, for soak: In a small microwave-safe bowl, stir together 3 tablespoons (45 grams) water, limoncello, and sugar. Heat on high in 15-second intervals, stirring between each, until sugar dissolves.
• Remove cake from oven, and using a long skewer, poke a few holes in top of cake. (Don’t poke all the way to the bottom of the pan.) Pour about half of soak onto cake. Let cool in pan for 15 minutes. Invert cake onto a wire rack, and pour remaining soak on top of cake. (The top of the cake should still be porous from baking, so pour the soak without poking to preserve the look of the cake.) Let cool completely on wire rack.
• When ready to serve, garnish with confectioners’ sugar, if desired. Store in an airtight container for up to 3 days.

Using a Conventional Mixer:

• For cake: In the bowl of a stand mixer, whisk together granulated sugar and lemon zest by hand until fragrant. Add butter; using the paddle attachment, beat at medium speed until light and fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add egg and egg yolk, one at a time, beating until combined after each addition. Beat in vanilla.
• In a medium bowl, whisk together flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with mascarpone and lemon juice, beginning and ending with flour mixture, beating just until combined after each addition and stopping to scrape sides of bowl.
• Lightly spray a 10-cup fluted tube pan with baking spray with flour. Spread batter into prepared pan. Firmly tap pan on a kitchen towel-lined counter to settle batter.
• Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers 205°F (96°C), 1 hour to 1 hour and 5 minutes.
• Meanwhile, for soak: In a small microwave-safe bowl, stir together 3 tablespoons (45 grams) water, limoncello, and sugar. Heat on high in 15-second intervals, stirring between each, until sugar dissolves.
• Remove cake from oven, and using a long skewer, poke a few holes in top of cake. (Don’t poke all the way to the bottom of the pan.) Pour about half of soak onto cake. Let cool in pan for 15 minutes. Invert cake onto a wire rack, and pour remaining soak on top of cake. (The top of the cake should still be porous from baking, so pour the soak without poking to preserve the look of the cake.) Let cool completely on wire rack.
• When ready to serve, garnish with confectioners’ sugar, if desired. Store in an airtight container for up to 3 days.