Preheat the oven to 350˚F/175°C. Line 2 8-inch round baking pans with parchment paper or grease well with cooking spray.
Make Vanilla Cake. In a large bowl, whisk flour, baking powder, baking soda and salt together to combine. Set aside.
In a large mixing bowl using an electric hand mixer (or stand mixer), beat the butter, oil and sugar on medium speed for 6 minutes until fluffy and light. Scrape the sides of the bowl. Add eggs, one at a time, beating well with each addition. Remember to scrape down the bowl as needed. Add vanilla extract and beat until combined.
On a medium speed, using the mixer to alternate adding flour mixture and buttermilk to the butter mixture, starting and ending with flour mixture as in order: flour-buttermilk-flour-buttermilk-flour. Beat until just combined after each addition. The batter should be smooth and completely incorporated. Avoid overmixing.
Divide batter evenly into your prepared cake pans, and bake on the center rack at 350˚F (175˚C) for 30-35 minutes, until the cake tester (or a toothpick) comes out clean. This means no wet batter remained in the cake.
Allow the cake to cook in cake pans for 10-15 minutes before transferring to cool completely on a wire rack. The cake must be cool completely or chilled in the fridge for at least 1 hour before applying frosting.
Make Buttercream Frosting. In the bowl of an electric mixer fitted with the paddle attachment, beat butter and salt on medium speed until smooth and creamy, about 2 minutes. Add 2 cups powdered sugar and beat until combined, then add another 1 cup, and beat until completely smooth. Add cream, vanilla, and lemon juice and beat on high speed for 2 minutes until light fluffy and thick enough to pipe.
Assemble Cake. Place one cake layer onto your serving plate. Spread an even layer of buttercream about 1-inch thick using a small offset palette knife or a piping bag. Place one cake layer on a cake board or a serving plate do a thin crumb coat on the cake. top with fresh berries or any kind of fruits you like (optional). Chill for at least 2 hours in the fridge. Slice and serve cold.