Preheat oven to 350°F Place oven rack in lowest position and generously butter a bundt pan.
Make Streusel: In small food processor, process flour, sugar, 1/4 cup of dark brown sugar, and cinnamon for 15 seconds. Remove 1-1/4 cups of mixture; add 1/4 cup dark brown sugar to it and set aside. Add cold butter and chopped pecans to mixture in food processor; pulse 10 times and set aside.
In small bowl, combine blueberries and lemon zest and set aside. In another bowl, whisk the eggs, 1 cup sour cream and vanilla together and set aside.
Mix the flour and rest of dry ingredients together until blended in mixer. Add the butter and remaining sour cream and blend on low until ingredients are moistened.
Gradually add egg mixture in 3 additions, beating 20 seconds after each addition. Increase speed and beat till batter is light and fluffy.
Spread 2 cups of batter in pan and top with 1/2 cup blueberries. Sprinkle with half of sugar streusel. Repeat layers. Spread with remaining batter and top with pecan streusel.
Bake 50 to 60 minutes or until toothpick comes out clean when inserted in the middle. Cool on wire rack 30 minutes. Invert out on plate and turn so streusel is on top. Cool 2 hours. Wrap in foil and store at room temperature.