Part 1: Baking the Lemon Cake Layers

1. Preheat and Prepare Pans: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Trace the bottom of the pans onto parchment paper, cut out the circles, and place them in the bottom of the greased pans. Grease and flour the parchment paper as well. This guarantees your cakes will not stick.

2. Whisk Dry Ingredients: In a large bowl, whisk together the 3 cups of all-purpose flour, baking powder, baking soda, and salt. Set aside.

3. Toss the Blueberries: In a separate small bowl, gently toss the fresh blueberries with 1 tablespoon of flour until they are lightly coated. This simple step helps prevent the blueberries from sinking to the bottom of the cake batter during baking.

4. Cream Butter and Sugar: In the bowl of a stand mixer fitted with a paddle attachment, or in a large bowl with a hand mixer, beat the softened butter, granulated sugar, and lemon zest on medium-high speed for 3-5 minutes. The mixture should become very light, pale, and fluffy. This step incorporates air into the batter, which is crucial for a light texture.

5. Add Oil and Eggs: With the mixer on medium speed, drizzle in the vegetable oil. Then, add the room-temperature eggs one at a time, beating well for about 30 seconds after each addition and scraping down the sides of the bowl as needed. Add the vanilla extract and mix to combine.

6. Alternate Wet and Dry: With the mixer on low speed, add the dry ingredient mixture in three additions, alternating with the buttermilk in two additions (begin and end with the dry ingredients: Dry-Wet-Dry-Wet-Dry). Mix only until just combined after each addition. It is crucial not to overmix the batter at this stage.

7. Fold in Blueberries: Gently fold the flour-coated blueberries into the batter using a rubber spatula.

8. Bake: Divide the batter evenly between the two prepared cake pans. Bake for 30-35 minutes, or until the centers are set and a wooden skewer inserted into the center comes out clean or with a few moist crumbs attached.

9. Cool: Let the cakes cool in their pans on a wire rack for 15 minutes before inverting them onto the rack to cool completely.

Part 2: Making the Lemon Simple Syrup

1. Combine Ingredients: While the cakes are cooling, prepare the syrup. In a small saucepan, combine the sugar, water, and fresh lemon juice.

2. Dissolve and Cool: Bring the mixture to a simmer over medium heat, stirring until the sugar is completely dissolved. Remove from the heat and let it cool.

3. Soak the Cakes: Once the cake layers are completely cool, use a pastry brush to lightly brush the lemon syrup over the tops of both cake layers. This adds an extra layer of lemon flavor and guarantees an ultra-moist cake.

Part 3: Whipping the Frosting and Assembling the Cake

1. Beat Butter and Cream Cheese: In a large bowl with a stand mixer or hand mixer, beat the softened cream cheese and softened butter together on medium-high speed for 3-4 minutes until completely smooth, combined, and fluffy. This is the most important step for avoiding lumpy frosting.

2. Add Sugar and Flavors: Turn the mixer to low and gradually add the sifted powdered sugar. Once it’s mostly incorporated, add the lemon zest, lemon juice, vanilla extract, and salt.

3. Whip to Perfection: Increase the mixer speed to medium-high and beat for another 2-3 minutes until the frosting is light, airy, and spreadable.

4. Assemble the Cake: Place one cake layer on your serving plate or cake stand. Top it with a generous layer of frosting (about 1 ½ cups), spreading it evenly. Carefully place the second cake layer on top.

5. Frost the Cake: Use the remaining frosting to cover the top and sides of the cake. For a rustic look, use the back of a spoon to create swirls. For a smoother look, use an offset spatula.

6. Chill and Garnish: Refrigerate the cake for at least 30 minutes to allow the frosting to set. Before serving, garnish with fresh blueberries, thin lemon slices, or extra lemon zest.