Mascarpone-Filled Cake with Sherried Berries

INGREDIENTS

• 4 cups mixed berries, cut if large
• 2 large eggs
• 1/2 teaspoon salt
• 1/2 cup Fino (dry) Sherry
• 1/2 cup sugar
• 2 cups sifted cake flour (not self-rising; sift before measuring)
• confectioners sugar
• 1 cup chilled heavy cream
• 1 cup well-shaken buttermilk
• 1 cup sugar
• 1/4 cup sugar
• 8 ounces mascarpone (1 cup)
• 1 teaspoon baking soda
• 1 teaspoon pure vanilla extract
• 1 teaspoon baking powder
• 1 stick unsalted butter, softened