Lemon Cake Preparation:

1. Preheat & Prep: Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.
2. Whisk Dry Ingredients: Combine flour, sugar, baking powder, baking soda, and salt in a large bowl.
3. Cream Butter & Sugar: In a separate bowl, cream together butter and sugar until light and fluffy.
4. Add Eggs & Vanilla: Beat eggs into the butter mixture one at a time, then stir in vanilla extract.
5. Combine Wet & Dry: Alternate adding the dry ingredients and milk to the wet mixture, starting and ending with the dry. Mix until just combined – do not overmix!
6. Fold in Zest & Juice: Gently fold in the lemon zest and lemon juice.
7. Bake: Divide batter evenly between prepared pans and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
8. Cool: Let cakes cool in pans for 10 minutes before inverting onto wire racks to cool completely.

Blueberry Cheesecake Layer:

1. Prep Blueberries: Rinse and gently pat dry fresh blueberries. If using frozen, do not thaw.
2. Beat Cream Cheese & Sugar: Beat cream cheese and sugar until smooth and creamy.
3. Add Eggs & Yolks: Add eggs and egg yolks one at a time, beating well after each addition.
4. Add Sour Cream & Flavorings: Beat in sour cream, lemon juice, and lemon zest.
5. Fold in Blueberries: Gently fold in prepared blueberries.
6. Prepare Water Bath: Wrap the bottom of a 9-inch springform pan tightly with foil. Place pan inside a larger roasting pan.

Lemon Cream Cheese Frosting:

1. Beat Cream Cheese & Butter: Beat cream cheese and butter until light and fluffy.
2. Add Powdered Sugar: Gradually add powdered sugar, beating well after each addition.
3. Flavorings: Mix in vanilla, lemon juice, and lemon zest.

Assembling the Cake:

1. Level Cakes (if needed): Use a serrated knife to level the tops of the lemon cakes if they domed during baking.
2. Layer 1: Cake & Cheesecake: Place one lemon cake layer on a serving plate. Top with the blueberry cheesecake mixture, spreading evenly.
3. Layer 2: Second Cake: Place the second lemon cake layer on top.
4. Chill: Refrigerate the cake for at least 4 hours, or preferably overnight, to allow the cheesecake layer to set.
5. Frost: Spread the lemon cream cheese frosting over the top and sides of the cake.
6. Decorate (optional): Garnish with fresh blueberries and lemon slices, if desired.