1. PREPARE PANS AND OVEN: Preheat the oven to 350°F. Spray the sides of three 6-inch pans (or two 8-inch pans) with nonstick cooking spray and fit a parchment paper circle into the bottom of each pan. Whisk together the flour, baking powder, baking soda, and salt in a large bowl. lightly, which is correct. 

2. CREAM THE BUTTER AND BUILD THE BATTER: Combine the granulated sugar and lemon zest in the bowl of a stand mixer fitted with the paddle attachment. Rub the zest into the sugar with your fingertips for 30 seconds until fragrant. Add the room-temperature butter and beat on medium speed until light and fluffy, about 2 minutes. Add the vegetable oil and beat for 3 more minutes. Add the eggs one at a time on low speed, mixing until each one incorporates. Add the vanilla and turn the mixer to medium speed for 1 minute.

3. ADD FLOUR AND LEMON MILK: Turn the mixer off and add the entire flour mixture at once. Mix on low speed until just barely combined — about 10 seconds. Slowly pour in the lemon milk mixture and continue mixing on low just until the batter comes together, about 30 seconds. Do not overmix. Toss the fresh blueberries with the 2 teaspoons of flour right in the measuring cup, then gently fold 2/3 of the flour-coated berries into the batter with a rubber spatula.

4. FILL PANS AND BAKE: Divide the batter evenly between the prepared pans. Distribute the reserved 1/3 of flour-coated blueberries across the top of each pan and gently press them just slightly into the batter. Bake for 30–35 minutes until a toothpick inserted into the center comes out clean or with just a few moist crumbs. Cool in the pans for 5 minutes, then turn the layers out onto wire racks to cool completely before frosting.

5. MAKE THE LEMON CREAM CHEESE BUTTERCREAM: Beat the room-temperature butter in a stand mixer on medium-high speed for 5 minutes until pale and creamy. Add about 1/3 of the powdered sugar and mix on low until combined. Add the lemon juice and continue mixing on low. Add the remaining powdered sugar and mix until the frosting looks thick and crumbly — this is normal. Add the room-temperature cream cheese and salt and mix on medium speed for 2–3 minutes until the frosting is completely smooth, silky, and stable.

6. FILL, STACK, AND FROST: Level the cake layers with a serrated knife if needed. Place the first layer on a cake board or stand and spread an even layer of lemon cream cheese buttercream over the top. Add the second layer and repeat. Place the final layer on top. Apply a thin crumb coat of buttercream all over the outside and refrigerate for at least 30 minutes to set. Apply the final coat of buttercream and smooth with an offset spatula and bench scraper. Pipe any remaining buttercream as a decorative border and garnish with fresh blueberries and lemon slices.