Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a loaf pan, or any pan with sides at least 4 inches high.

Beat sugar and butter using an electric mixer in a large mixing bowl until creamy, scraping the bowl often with a rubber spatula. Continue to beat, adding eggs 1 at a time, until well combined.

Combine flour, baking powder, baking soda, and salt in a separate bowl.

Reduce mixer speed to low and continue beating the sugar mixture. Gradually add flour mixture alternatively with buttermilk until well combined, 2 to 3 minutes. Add lemon zest and lemon extract; mix well. Spread pound cake crust mixture into the prepared pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 55 to 60 minutes.

Let pound cake cool completely. Cut cake into pieces and press into the bottom of a 10-inch springform pan. Set aside.

Preheat the oven to 350 degrees F (175 degrees C).

Beat cream cheese and sugar using an electric mixer in a large mixing bowl until fluffy. Add eggs 1 at a time, beating well after each addition. Add lemon pudding, sour cream, and lemon zest; blend well. Pour filling into prepared crust and spread evenly.

Fill an oven-safe container with water and place it in the preheated oven under the rack where you will place the cheesecake; this will prevent cracking.

Bake cheesecake in the preheated oven until almost set, about 45 minutes.

Meanwhile, beat egg whites, cream of tartar, and salt together in a bowl using an electric mixer until soft peaks form. Pour in sugar while beating constantly until glossy peaks form.

Remove cheesecake from oven, leaving oven on. Spread meringue topping over the filling to edges, using a spatula to tap for desired peaks. Return cheesecake immediately to oven.

Continue to bake cheesecake until meringue is golden brown, 14 to 15 minutes. Turn off the oven. Crack the oven door open, and let cheesecake set and slowly cool for 15 minutes.

Remove from oven and let cheesecake cool completely, 20 to 30 minutes more. Refrigerate 8 hours to overnight.