Heat oven to 350. Grease a 10" angel food cake pan or any other 10" tube pan, preferably with a removable bottom.
For streusel: In a medium bowl, stir brown sugar, flour, nuts and cinnamon to mix. Add butter and stir with a fork or rub into dry mixture with fingertips until crumbly.
For cake: Beat butter in a large bowl with an electric mixer on medium speed until fluffy, about 3 minutes. Add sugars, one at a time and beat until well blended. Add eggs, one at a time, beating until blended after each. Reduce mixer speed to low and beat in vanilla, baking powder, baking soda and salt. Beat in half the flour, then the sour cream. When blended, beat in remaining flour.
Spread half the batter in the prepared pan. Top with half the streusel. Carefully spoon on remaining batter, spread smooth and crumble remaining streusel over the top. Gently press streusel so it will adhere to cake.
Bake 1 hour 10 minutes or until a wooden pick inserted in center of cake comes out clean. Place pan on a wire rack and let cool completely. Fun a knife around the edges and tube to loosen cake. If pan has a removable bottom, remove pan, run a knife around base of cake and remove tube. If pan doesn't have a removable bottom, place a plate on top of pan and holding plate and pan together, carefully invert cake onto the plate, then turn cake right side up.