Red Velvet Cake with Raspberries and Blueberries

INGREDIENTS

• 1 1/2 cups sugar
• 1/2 teaspoon salt
• 2 1/4 cups sifted cake flour (sifted, then measured)
• 1 cup buttermilk
• 1/2 cup (1 stick) unsalted butter, room temperature
• 3 1/2-pint baskets fresh raspberries
• 1 teaspoon vanilla extract
• 3 1/2-pint baskets fresh blueberries
• 2 large eggs
• 1 teaspoon baking soda
• 2 1/2 cups powdered sugar
• 2 tablespoons unsweetened cocoa powder
• 1 tablespoon red food coloring
• 1 teaspoon baking powder
• 1 tablespoon vanilla extract
• 2 8-ounce packages cream cheese, room temperature
• 1 teaspoon distilled white vinegar