1-Preheat oven: Preheat oven to 325°F. Line two 8-9 inch round baking pans with parchment paper and spray with nonstick cooking spray.

2-Whisk dry ingredients: Whisk flour, baking powder, baking soda, and salt in a large bowl; set aside.

3-Stir wet ingredients: Stir milk and vanilla extract together in a liquid measuring cup; set aside.

4-Beat butter mixture: In a large bowl, beat softened butter, vegetable oil, and sugar with an electric mixer until combined.

5-Add eggs: Add eggs and egg whites one at a time; beat until light and fluffy. Scrape bowl and mix briefly.

6-Combine mixtures: Alternately add the dry flour mixture and milk mixture to the wet mixture, starting and ending with dry ingredients. Mix until smooth, avoiding overmixing.

7-Bake batter: Divide batter evenly between pans and smooth tops. Bake 30-40 minutes in the lower two-thirds of the oven until a toothpick inserted comes out clean or with a few moist crumbs.

8-Cool cakes: Cool cakes in pans for 15-20 minutes, then invert onto racks to cool completely.

9-Prepare whipped cream: Whip heavy cream, vanilla extract, and powdered sugar until stiff peaks form. Set aside half for frosting. Gently fold diced strawberries into the remaining whipped cream for filling.

10-Cut layers: Cut each cake layer horizontally in half to create four thin layers.

11-Layer cake: Place one cake layer on a serving platter. Spread one-third of the strawberry cream filling over it. Repeat layering with remaining cake layers and filling.

12-Frost cake: Frost the outside of the cake with the reserved plain whipped cream. Decorate the top with sliced strawberries.

13-Refrigerate: Refrigerate for at least four hours, preferably overnight, to set before serving.