Glorious Red, White, and Blue Cake

Ingredients

• 0.5 teaspoon baking soda 
• 6 ounces blackberries 
• 12 ounces blueberries 
• 1.3 cups cake flour sifted (sift before measuring)
• 1.5 teaspoons cider vinegar white
• 0.3 cup natural cocoa unsweetened (such as Hershey's; not Dutch process or extra-dark cocoa)
• 3.3 cups confectioners' sugar 
• 8 ounce cream cheese softened (20 ounces total)
• 3 large egg whites 
• 2 large eggs 
• 0.8 cup granulated sugar 
• 2.5 tablespoons juice of lemon fresh
• 1 tablespoon lemon zest with microplane zester or grater) grated
• 1 ounce food coloring red (2 tablespoons)
• 0.3 teaspoon salt 
• 0.3 cup cup heavy whipping cream mixed sour with 2 tablespoons water
• 0.8 cup cup heavy whipping cream mixed sour with 1/4 cup water
• 1.3 cups butter unsalted softened
• 2 teaspoons vanilla extract 
• 0.3 cup vegetable oil 
• 8 ounces quarter if 

Equipment

• bowl
• frying pan
• oven
• knife
• whisk
• hand mixer
• cake form
• stand mixer
• ziploc bags
• wax paper
• pastry brush

Directions

1. Heat oven to 350°F. Butter two 9-inch round cake pans, then line bottoms with rounds of wax paper. Butter paper and dust pans with some additional flour, knocking out excess.
2. Resift cake flour together with cocoa, baking soda, and salt into a bowl.
3. Beat butter and sugar in a large bowl with an electric mixer (fitted with paddle attachment if using stand mixer) at medium-high speed until combined well, then add oil and beat until very pale and creamy, about 3 minutes.
4. Add eggs, one at a time, beating well after each addition, and beat in food coloring, vinegar, and vanilla extract.
5. Reduce speed to low and mix in flour mixture and sour cream mixture in batches, beginning and ending with flour mixture, and mixing until batter is smooth.
6. Divide batter between pans (about 3 cups in each) and smooth tops. Rap pans on counter a couple of times to expel any air bubbles.
7. Bake in middle of oven until a wooden pick comes out clean and cake begins to pull away from sides of pans, 25 to 30 minutes. Keep oven on.
8. Cool layers in pans on racks 10 minutes, then run a thin knife around edge of pans. Invert layers onto racks and peel off wax paper. Cool layers completely.
9. Butter one 9-inch round cake pan, then line bottom with wax paper. Butter paper and dust pan with some additional flour, knocking out excess.
10. Resift cake flour together with baking soda and salt into a bowl.
11. Whisk egg whites in another bowl with sour cream mixture until combined.
12. Beat butter and sugar in a large bowl with an electric mixer (fitted with paddle attachment if using stand mixer) at medium-high speed until combined well, then add oil and beat until very pale and creamy, about 3 minutes. Beat in zest and vanilla extract.
13. Reduce speed to low and mix in flour mixture and sour cream mixture in batches, beginning and ending with flour mixture and mixing until batter is smooth.
14. Transfer batter to pan and spread evenly. Rap pan on counter a couple of times to expel any air bubbles.
15. Bake in middle of oven until a wooden pick comes out clean and cake begins to pull away from side of pan, 25 to 30 minutes. Cool in pan on a rack 10 minutes, then run a thin knife around edge of pan. Invert layer onto rack and peel off wax paper. Cool layer completely.
16. Beat together cream cheese and butter in a large bowl with an electric mixture until creamy and smooth. Beat in lemon juice, vanilla extract, and salt.
17. Sift confectioners' sugar into a bowl and add to cream cheese mixture.
18. Mix on low speed until incorporated, then increase speed to medium-high and beat until smooth.
19. Brush loose crumbs from cake layers with a pastry brush.
20. Put a red velvet layer, bottom side up, on a cake plate or stand.
21. Spread 1 cup of frosting over layer. Cover with white layer, bottom side up, and spread with another cup of frosting. Top with second red velvet layer, bottom side up.
22. Spread a thin layer of frosting around sides and over top of cake. (This is called crumb-coating. It tamps down any loose crumbs to keep them out of the top layer of frosting and fills in any crevices. This is particularly important with red velvet cake layers.) Chill or briefly freeze cake just until frosting is firm.
23. Spread sides and top of cake with remaining frosting. Chill or briefly freeze cake just until frosting is firm.
24. Toss together fruits in a bowl.
25. Let cake come to room temperature before serving and top with about 1 1/2 cups fruit.
26. Serve remaining fruit on the side.
27. Cake layers can be made 1 day ahead and chilled or 1 week ahead and frozen. Wrap well in wax paper and then in a heavy-duty sealable plastic bag. No need to thaw before assembling cake (cake is easier to frost when layers are chilled or frozen), but allow plenty of time for cake to thaw and come to room temperature after frosting it. Cake can be frosted 1 day ahead and kept in a cake keeper, chilled. Bring to room temperature.