Heat oven to 350°.
Grease and flour a bundt pan very well.
Beat ½ cup softened butter in large bowl with an electric mixer until creamy; add 1 cup granulated sugar, and beat until fluffy.
Beat in egg and vanilla.
Whisk together 2 cups flour, baking powder, and salt add alternately with the milk to the creamed mixture, beating well after each addition.
Spread half the batter in the prepared pan.
Cover with berries, and add remaining batter by tablespoons.
Cover with streusel topping.
Bake at 350° for 55-60 minutes, until deep golden brown.
If knife or bamboo skewer inserted in center comes out clean, cake is done.
Remove pan to wire rack to cool.
Invert onto a plate after cake has cooled, and dust with powdered sugar.