1- First, preheat your oven to 350°F and prepare your baking pans by greasing and lining two 9-inch cake pans with parchment paper. Use baking strips for even baking to ensure your Chantilly Cake layers come out flat and perfect. In a bowl, sift the cake flour and baking powder, then add salt and whisk everything together for even distribution.

2- Next, in a separate bowl, beat the softened butter until it’s creamy, then add the granulated sugar and beat until the mixture is light and fluffy. This step is crucial for incorporating air and achieving that tender texture. Add the eggs one at a time, mixing well after each, followed by the vanilla extract to build the base flavor.

3- Now, alternate adding the flour mixture, vegetable oil, and whole milk to the batter, mixing until just combined to keep the batter smooth and airy. Divide the batter evenly between the prepared pans, smooth the tops, and bake for 40 to 45 minutes, or until the cakes are golden and the sides pull away from the pans.

4- While the cakes cool, make the berry filling by warming the seedless berry jam and water in a pan, then stirring in sliced strawberries, raspberries, blueberries, and the juice and zest of one lemon. For the Chantilly cream, beat the mascarpone and cream cheese until smooth, gradually add the sifted powdered sugar, and beat until fluffy.

5- In another bowl, whip the cold heavy whipping cream with vanilla extract until stiff peaks form, then gently fold it into the cheese mixture. Once the cakes have cooled completely in their pans for about 20 minutes and then on a wire rack, cut each layer in half horizontally to create four layers.

6- To assemble, place one cake layer cut-side up, spread one-third of the berry mixture thinly over it, add about 3/4 cup of Chantilly cream, and top with one-third of the fresh berries. Repeat for the remaining layers, then spread 1 cup of Chantilly cream over the top and sides, and pipe the rest decoratively. Garnish with fresh berries and refrigerate for at least 2 hours before serving. Remember, keeping the heavy whipping cream cold is key to avoiding runny frosting; if it happens, chill and re-whip it.