Preheat oven to 350°F. Line a 1 lb tube pan with bottom parchment paper, grease sides and tube center with butter. Set aside.
In a large bowl, cream butter and sugars until light and fluffy. Add eggs and vanilla extract; mix thoroughly.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt. In another bowl, combine sour cream and milk.
Gradually fold the flour mixture and sour cream-milk blend into wet ingredients until fully combined, no flour streaks left.
Add blueberries and white chocolate chips. Gently fold to distribute; avoid overmixing.
For streusel, mix all ingredients until it resembles wet sand and clumps.
Pour batter into the prepared pan, top with streusel (squeeze it to make it dense like wet sand), and sprinkle over the batter.
Bake for 50 minutes to 1 hour, then let it cool slightly before removing from the pan. Allow the cake to cool.
While the cake cools, prepare the icing. Combine all frosting ingredients in a small bowl, mix, and drizzle over the cooled bundt cake. Enjoy!