In a stand mixer fitted with a paddle attachment, cream together softened butter, granulated sugar and brown sugar on medium-high speed until light and fluffy (about 4 minutes). Add eggs, one at a time, beating until completely combined. Mix in sour cream and vanilla extract.
In a separate bowl, sift together flour, baking powder, baking soda and salt. While the mixer is running on low speed, gradually add the dry ingredients to the wet ingredients. Mix just until combined – do not overmix.
Sprinkle half of the streusel mixture in the prepared pan. Top with half of the batter. Add remaining streusel, and then remaining batter.
Bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean. Cool cake in pan on a wire rack 15 minutes; invert cake onto wire rack, and let cool completely before glazing (about 2 hours).