Preheat oven to 300 degrees F. Line the entire inside of a 9-inch cake pan with aluminum foil. Press it into the pan to get it as flat as you can. You’ll use the aluminum foil to lift the cheesecake out of the pan when it’s baked and cooled.
In a large mixer bowl, mix the cream cheese, sugar and flour together until combined. Use low speed to keep less air from getting into the batter, which can cause cracks. Scrape down the sides of the bowl.
Add the sour cream, and vanilla extract and mix on low speed until well combined.
Add the eggs one at a time, mixing slowly and scraping the sides of the bowl after each addition.
Pour the cheesecake batter into the lined cake pan.
Place the cake pan inside another larger pan. I use a larger cake pan, but you can use a roasting pan or any other larger baking pan. Fill the outside pan with enough warm water to go about halfway up the sides of the cake pan. Bake for 1 hour.
Turn off the oven and leave the cheesecake in the oven with the door closed for 30 minutes. Do not open the door or you’ll release the heat.
Crack oven door and leave the cheesecake in the oven for another 30 minutes. This cooling process helps the cheesecake cool slowly to prevent cracks.
Remove cheesecake from oven and chill until firm, 5-6 hours.
For the Lemon Cake
Preheat the oven to 350 degrees F. Spray or grease two 9-inch round cake pans. Cut out 9-inch parchment paper circles and press down in the bottom of each pan. (Trace the pan for perfect circles.)
In the bowl of your stand mixer, cream the butter and sugar together until light and fluffy. (Beat on high approximately 3-5 minutes to break down the sugar crystals.)
In a separate bowl, mix the cake flour, baking powder, baking soda, and salt.
Once the butter and sugar are well creamed. Scrape the mixing bowl with a rubber spatula. Then turn the mixer on low and beat in the eggs, lemon zest, vanilla extract, lemon extract, and yellow food coloring if using.
Scrape the bowl again. Turn the mixer back on low and alternate adding the flour mixture and buttermilk until both are well combined. Turn off the mixer.
Pour the batter evenly into the two prepared pans. Bake on the middle rack, undisturbed for 30 minutes.
Check the cake by inserting a toothpick into the center. If it comes out clean, take them out of the oven. If the toothpick has batter on it, bake another 5-10 minutes and recheck.
Allow the cakes to cool 10 minutes in the pans. Then carefully flip them out on a cooling rack. Remove the parchment paper and cool completely.
For the Lemon Buttercream
Once the cakes are room temperature, place the butter in a clean stand mixer bowl. Beat until fluffy. Then scrape the bowl and turn on low. Mix in the buttermilk and lemon juice. Then add the powdered sugar one cup at a time, beating to incorporate.
After adding powdered sugar, turn the mixer up to beat out any clumps. Check the consistency of the frosting. If it is too loose, add another 1-2 cups of powdered sugar and beat until smooth.
Assembling the Cake
Move one cake to a cake stand or platter. Scoop about 1 cup frosting onto the cake. Use a large flat spatula to spread the frosting out evenly.
Use the aluminum foil to lift the cheesecake out of the cake pan, remove the foil and place the cheesecake on top of the cake.
Spread another cup of frosting evenly on top of the cheesecake, then add the second layer of cake on top.
Gently press the cake a little to level the top. Then scoop all remaining frosting on top of the cake. Use the spatula to work the frosting over the top and down the sides.
Use a spoon to make swooping marks on sides and tops of cake for a rustic look. Use a wet paper towel to clean up the cake stand.