Preheat Oven & Prepare Pans – Preheat oven to 350°F (175°C). Grease three 8-inch round cake pans and line with parchment paper.

Mix Wet Ingredients – In a stand mixer, beat applesauce, buttermilk, vanilla, and egg whites for 2 minutes. Add sour cream and mix until combined.

Combine Dry Ingredients – In a separate bowl, whisk flour, sugar, baking powder, baking soda, salt, and pudding mix.

Make the Batter – Gradually add dry ingredients to wet mixture, mixing until just combined. Do not overmix.

Bake the Cake Layers – Divide batter evenly among the prepared pans. Bake 20–25 minutes, or until a toothpick inserted in the center comes out clean with moist crumbs. Cool completely on wire racks.

Prepare the Frosting – Melt white chocolate chips with butter; let cool until slightly warm. Beat mascarpone until light, add cooled chocolate and vanilla, then gradually mix in powdered sugar. Add heavy cream for desired consistency; beat until fluffy.

Prepare the Cream Topping – Whisk pudding mix with milk until thick. In another bowl, whip heavy cream with powdered sugar until stiff peaks form. Fold whipped cream into pudding mixture, adding stabilizer if desired.

Assemble the Cake – Place one cake layer on a serving plate. Spread frosting evenly, add a layer of berries. Repeat with the second layer. Place the third layer on top and frost the entire cake.

Add Cream Topping & Decorate – Swirl cream topping over the cake with a spatula or spoon. Decorate with extra fresh berries. Chill for at least 15 minutes before serving.