Start by preparing and cooling the raspberry sauce. This step is essential as the raspberry sauce must be completely cooled before using. To make the sauce, combine raspberries, granulated sugar, and lemon juice in a small saucepan over medium heat. Cover and cook for about 3 minutes until the berries are thawed and begin to break down. Stir the mixture while it simmers, breaking up some of the raspberries as you go.

Once the raspberries have broken down and are simmering, mix the water and cornstarch in a small bowl to form a slurry. Add this cornstarch mixture to the raspberry mixture, stirring it in. Continue to cook and stir until the sauce begins to bubble and thicken. Remove from heat and strain the sauce through a fine mesh sieve to remove seeds, if desired (I prefer to leave the seeds in). Allow the raspberry sauce to cool completely, then chill it for at least 30 minutes before using. It can be covered and stored in the refrigerator for up to a week.

Preheat the oven to 350°F (175°C). Line the bottom of two 8-inch round cake pans with parchment paper. I typically skip greasing the pans, as I like the batter to cling to the sides for more height, but feel free to lightly grease the sides if you prefer.

For the cake batter, sift the flour, baking powder, baking soda, and salt into a medium bowl, then whisk to combine. In a large bowl, beat the softened butter, oil, sugar, and vanilla with an electric hand mixer for 2 minutes until pale and fluffy. Add the egg and beat until fully incorporated. Next, add the egg whites and mix until smooth. Stir in the sour cream. Sift half of the flour mixture over the wet ingredients and mix slowly, followed by half of the milk. Add the remaining flour mixture, then the rest of the milk. Beat on high for about 5 seconds to emulsify the batter. Finally, gently fold in the raspberries.

Divide the batter evenly between the prepared pans and bake for 25-30 minutes, until lightly golden and a skewer inserted into the center comes out clean. Let the cakes cool in the pans on a wire rack for 20-30 minutes, then run an offset spatula or knife around the edges to loosen the cakes. Invert the cakes, remove the bottom layer of parchment, and let them cool completely on the rack.

For the frosting, place chopped white chocolate in a large bowl. Heat ½ cup of cream in a saucepan over medium heat with the scraped vanilla bean seeds (and I also add the scraped pod, as it still contains many seeds). Once the cream comes to a simmer, pour it over the chopped chocolate, cover the bowl, and let it sit for 2 minutes. Uncover and whisk until the chocolate is fully melted and the mixture is smooth and silky. Let it cool for 5 minutes, then whisk in the remaining cold cream. Refrigerate the bowl for at least 2 hours or overnight until the mixture is completely cold. If chilling overnight, cover the bowl after 20 minutes. You can also prepare the frosting base first and bake the cake layers the following day.

Once chilled, add the vanilla extract and beat with an electric hand mixer or stand mixer fitted with the whisk attachment on medium speed for about 2 minutes, or until thick and fluffy. The consistency should resemble soft peaks (check the video for reference).

To assemble the cake, place one layer of cake on a serving plate. Fill a piping bag with about 1 cup of frosting and pipe it around the circumference of the cake to form a border. This will help keep the raspberry filling from spilling out. Use a small offset spatula to spread 1 cup of raspberry filling inside the frosting border. Place the second layer of cake on top, aligning it with the edges of the bottom layer. Cover the entire cake with frosting, smoothing the sides with a large offset spatula and adding swirls to the top. Optional: dollop small spoonfuls of raspberry sauce on top and swirl them in for decoration. Finish by decorating with fresh raspberries.