Preheat the oven to 325 degrees F. Grease and flour a Bundt pan, then set it aside.
In the bowl of a stand mixer, beat together 1 cup unsalted butter, 8 ounce cream cheese, and 2 3/4 cups granulated sugar until fluffy, about 1-2 minutes.
Add 6 large eggs, one at a time, mixing after each addition. Then mix in 1/2 cup sour cream and 1 tablespoon vanilla extract until evenly combined. Scrape the sides of the bowl as needed.
In a medium mixing bowl, stir together 3 cups cake flour, 1 teaspoon baking powder, and 1/4 teaspoon salt. Add the flour mixture to the wet ingredients in two additions, mixing until just combined each time.
Pour the cake batter into the prepared Bundt pan. Bake for 75 minutes or until a toothpick inserted halfway between the tube and the pan wall comes out clean.
Remove the cake and let it cool in the pan for 10 minutes. Then invert it onto a wire rack or serving platter. Allow to cool completely. Cut into 10 slices and serve with whipped cream and fresh berries if desired.
Notes
Cake flour substitute: 2 ½ cups + 2 tablespoons all-purpose flour mixed with 6 tablespoons cornstarch.For the best texture, use room-temperature butter, cream cheese, and eggs so the batter mixes smoothly.Check doneness by inserting a long skewer halfway between the center tube and the pan wall.