1. Preheat oven to 350F/177C. Grease two 9×2 inch (23×5 cm) round baking pans and line with parchment. Place in refrigerator.
2. Sift cake flour into medium bowl, measure 2 1/4 cups (214 grams), then sift flour with cocoa powder, baking soda, baking powder, and salt into a large bowl.
3. Combine buttermilk, sour cream, food coloring, vanilla, and vinegar in a liquid measuring cup or small bowl. Whisk until smooth.
4. With a stand mixer fitted with the paddle attachment, cream the butter and sugar on medium speed until fluffy, about 4-5 minutes. Add eggs, one at a time, blending well after each addition, scraping down the bowl with a spatula as needed. Add the flour mixture in 4 batches, alternating with the buttermilk mixture, beginning and ending with the flour.
5. Divide batter between the cake pans. Bake 24-29 minutes, or until an inserted toothpick or cake tester comes out clean. Cool for ten minutes in the pans, then invert onto wire racks, remove parchment, and cool completely.

Cream Cheese Frosting

1. With a stand mixer fitted with the paddle attachment, beat the cream cheese and butter until blended. Add the vanilla and beat to blend. Add confectioners’ sugar and slowly mix to blend, then increase speed to medium for 1 minute.

To Assemble

1. Place one cake layer, bottom/flat side up onto a platter or cake stand. Frost top with a generous cup of cream cheese frosting, then top with 1 package of raspberries and 1/2 package blueberries, pressing lightly. Top with second cake layer, domed side up. Spread remaining frosting over top and sides of cake. Arrange berries decoratively on the top.
2. Store cake covered in refrigerator (can make the day before – let stand 1 hour before serving).
3. If desired, dust with confectioners’ sugar before cutting and serving.