Preheat oven to 350°F (177°C) and prepare two 9-inch round cake pans with non-stick spray and parchment paper.

In a medium bowl, whisk together the dry ingredients: cake flour, baking powder, baking soda, and salt.

In a stand mixer, beat together the butter and sugar until light and fluffy, about 3–5 minutes.

Add egg whites one at a time to the butter mixture, beating until just combined.

Mix in vegetable oil and vanilla extract, then alternately incorporate the dry mixture and buttermilk until smooth.

Divide batter between the prepared pans and bake for 28–32 minutes until a toothpick comes out clean.

Let the cakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Prepare the filling by combining berry jam with fresh berries, lemon juice, and zest.

Beat mascarpone and cream cheese until creamy, add powdered sugar, and fold in heavy whipping cream.

Level the cooled cake layers, stack them with berry jam and frosting in between, and apply a thin crumb coat.

Chill the cake for 30 minutes, then frost the outside with remaining mascarpone frosting and garnish with fresh berries.