• Preheat oven to 350°F.
• Grease and flour a 8 X 8 baking dish or a 9 inch spring form pan.

For the Streusel and Filling

• Whisk brown sugar, sugar, cinnamon and pecans together. Set aside ¾ cup for the filling.
• Add flour, butter and vanilla to the remaining mixture and form a crumbly streusel like topping.

For the Batter

• In a small bowl, gently mix egg yolks, approximately ⅜ cup of the sour cream and vanilla. Set aside.
• In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
• Add butter and remaining sour cream. Mix until well combined.
• Gradually add egg mixture slowly, a little at a time. Mix well after each time. Batter will be thick and sticky.
• Put about ⅔ of batter in prepared baking dish. Make sure to smooth the batter on top with a spatula.
• Sprinkle the filling over the top of the batter.
• Add blueberries over the filling.
• Add remaining batter on top of blueberries, in sections, and carefully smooth over the top of blueberries making sure that the blueberries and filling stay in place.
• Add stresuel topping.
• Bake for 55- 60 minutes or until tooth pick inserted into the center comes out clean.
• Set on a cooling rack to cool.