Preheat your oven to 350°F (175°C) and prepare two 8-inch cake pans with baking spray and parchment paper.

In a medium bowl, sift together all-purpose flour, cornstarch, baking powder, baking soda, and salt.

In a large bowl, cream together softened unsalted butter, canola oil, and white granulated sugar until fluffy.

Mix in vanilla paste, egg whites, and sour cream until thoroughly combined.

Gradually add the dry ingredients and buttermilk to the butter-sugar mixture and mix until just combined.

Divide batter between the prepared pans and bake for 35-40 minutes until golden brown.

Let the cakes cool in the pans for about 10 minutes before transferring to a wire rack.

Prepare the berries by tossing diced strawberries with blackberries and blueberries, adding sugar and letting sit for 10 minutes.

In another bowl, combine cream cheese, powdered sugar, and cold heavy cream and beat until creamy.

Whip additional cold heavy cream with powdered sugar and vanilla until soft peaks form, then fold into the cream cheese mixture.

Assemble the cake by layering whipped cream and macerated berries between the cake layers, then chill before serving.