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

In a stand mixer, cream together 1 cup unsalted butter and 2 cups granulated sugar until light and fluffy.

Add 4 eggs, 1 cup sour cream, and ½ cup vegetable oil; mix on medium-low until well combined.

In a separate bowl, whisk together 2 ½ cups cake flour, 2 ½ teaspoons baking powder, and a pinch of salt.

Combine 1 cup buttermilk, juice of 2 lemons, and zest from those lemons; pour into the mixer in increments, alternating with the dry mix.

Gently fold in 1 ½ cups fresh blueberries.

Divide the batter among the three pans and smooth the tops. Bake for 35-40 minutes until a toothpick comes out clean.

Cool the cakes in the pans for 15 minutes, then turn out onto wire racks to cool completely.

Beat 1 cup unsalted butter and 8 ounces cream cheese until smooth. Gradually add 4 cups powdered sugar, salt, and juice and zest of 1 lemon.

Stack cooled cake layers with frosting in between, apply a crumb coat, and refrigerate for 30 minutes.

After chilling, frost the exterior of the cake with a thicker layer of frosting.

Decorate with lemon slices and blueberries if desired before serving.