In a blender or food processor, puree strawberries, raspberries, and sugar together. With a sieve, drain the puree to remove all of the seeds. Set aside.

Preheat oven to 350 degrees and grease three 9" cake pans or line with parchment paper.

Separate the 4 Eggland's Best eggs and set aside.

In a large bowl, cream butter until light and fluffy, about 1-2 minutes. Add in vegetable oil and beat for another minute.

Gradually add in sugar, ½ cup at a time, beating until well combined. Add in egg yolks, one at a time, beating well after each addition.

In a separate bowl, sift together flour, cornstarch, baking powder, and salt. Set aside.

In a small bowl, mix together milk, vanilla extract, and sour cream.

Alternately add dry and wet ingredients into the creamed butter mixture, beginning and ending with the dry ingredients. Stir until just combined.

Beat egg whites until they form stiff peaks. Gently fold egg whites into the cake batter until completely combined.

Divide batter evenly in cake pans.

Dollop 4-5 tablespoon of puree in each cake pan, using a toothpick or knife to swirl the puree with the batter.

Bake for 25-30 minutes, or until a cake tester comes out clean. Allow to cool.

With a mixer on high, beat heavy whipping cream until it begins to thicken. Add in lemon zest, powdered sugar, and vanilla extract, and beat until soft peaks form.

Add whipped cream cheese to the whipped cream, and beat until well incorporated and stiff peaks form.

Once cakes are cooled, remove from the cake pans. Place the bottom layer on a flat plate or cake stand and top with about 1 cup of lemon whipped cream, spreading almost to the edges. Place a few raspberries and strawberries evenly throughout the cream.

Place the second layer on top and top with about 1 cup of lemon whipped cream, spreading almost to the edges, and add raspberries and strawberries.

Place the final layer on top and spread the remaining whipped cream on top.

If any of the cream has come out of the sides of the cake, use a spatula to smooth the cream around the cake.