Preheat your oven to 350°F (177°C). Prepare three 8-inch round cake pans—grease them well and line the bottoms with parchment paper, then grease the parchment too.

In a large mixing bowl, beat the softened butter on high speed for 1 minute until creamy. Add the granulated and brown sugars and continue beating for 2 minutes until fluffy.

Slowly drizzle in the vegetable oil, beating for another 3 minutes until light and creamy. Add in the eggs and vanilla extract, mixing on medium speed for 1 minute.

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. This helps to evenly distribute the leavening agents.

Gradually add the dry ingredients to the wet mixture, beating on low speed just until combined. Fold in the buttermilk, lemon zest, and lemon juice until incorporated.

Toss the blueberries in 1 tablespoon of flour before gently folding them into the batter to prevent sinking.

Divide the batter evenly among the prepared pans and bake for 22–26 minutes. Let them cool completely in the pans.

While the cakes cool, make the frosting by beating together the cream cheese and butter on medium speed for about 3 minutes until smooth.

Gradually add the confectioners' sugar, heavy cream, vanilla, and salt, beating on low speed before increasing to high for about 3 minutes.

Level the cake layers if domed. Place the first layer on a cake stand, spread frosting on top, repeat with remaining layers.

Use the remaining frosting to cover the top and sides of the cake. Chill for at least 45 minutes before slicing.