Preheat and Prepare: Preheat your oven to 350°F (175°C). Generously grease and flour a Bundt pan, ensuring all nooks and crannies are covered to prevent sticking.

Mix Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

Cream Butter and Sugar: In a large bowl, using an electric mixer, cream together the butter and granulated sugar until light and fluffy. Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.

Combine With Dry Ingredients: Alternately add the dry ingredients and sour cream to the butter mixture, beginning and ending with the dry ingredients. Stir in the melted white chocolate until just combined.

Fold in Berries: Gently fold the mixed berries into the batter, being careful not to crush them.

Bake: Pour the batter into the prepared Bundt pan. Smooth the top with a spatula. Bake for 45-50 minutes, or until a toothpick inserted into the cake comes out clean. Allow the cake to cool in the pan for 10 minutes, then turn out onto a wire rack to cool completely.

Prepare the Glaze: Combine the white chocolate chips and heavy cream in a small saucepan over low heat. Stir until the chocolate is melted and the mixture is smooth. Allow to cool slightly, then drizzle over the cooled cake.

Garnish and Serve: Just before serving, top the cake with additional fresh berries and a dusting of powdered sugar if desired.