Preheat your oven to 350℉ (177℃) and line cupcake pans with liners.

In a large mixing bowl, whisk together cake flour, baking powder, and salt.

In a separate bowl, cream the granulated sugar, unsalted butter, and vegetable oil until light and fluffy.

Mix in the egg whites, sour cream, vanilla extract, and vanilla bean paste.

Gradually add the dry mixture to the wet ingredients, alternating with milk, until smooth.

Fill each cupcake liner two-thirds full and bake for 20 minutes.

Beat together mascarpone cheese, powdered sugar, and vanilla until smooth; then mix in heavy whipping cream until medium-stiff peaks form.

Combine mixed berries, sugar, and lemon juice in a saucepan; once bubbling, add cornstarch mixed with water and cook until thickened.

Create a well in each cooled cupcake, fill with berry mixture, and top with Chantilly cream frosting and fresh berries.