Preheat your oven to 335°F (170°C) and prepare three 7-inch cake pans with cooking spray and parchment paper.

Cream together unsalted butter and granulated sugar in a stand mixer on medium speed for about 2 minutes.

Add eggs, sour cream, and vegetable oil to the butter-sugar mixture and mix until smooth, about 1-2 minutes.

In a separate bowl, whisk together cake flour, baking powder, and salt.

Combine the buttermilk, lemon juice, and lemon zest in a measuring cup. Alternate adding the dry mixture and buttermilk mixture to the wet ingredients until just combined.

Fold in fresh blueberries gently using a spatula.

Divide the batter evenly among the prepared pans and bake for 35-40 minutes or until a toothpick comes out clean.

Let the cakes cool in the pans for 15 minutes and then invert onto a wire rack to cool completely.

Beat cream cheese and unsalted butter until smooth. Gradually add powdered sugar, salt, lemon juice, and zest, mixing until fluffy.

Layer frosting between each cake layer and spread around the outside. Chill for 30 minutes before garnishing with lemon slices and blueberries.