Adjust the oven rack to the lowest position and heat the oven to 350 degrees. Grease the inside of a 10 inch pan.
For the Steusel - Place the flour, granulated sugar, 1/4 cup dark brown sugar, and the cinnamon in a food processor and pulse a few times to combine. Transfer 1 1/4 cups of the mixture to small bowl and stir in remaining 1/4 cup brown sugar; set aside (this will be the streusel for the inside of the cake). Add the butter and pecans to the remaining dry ingredients in the food processor bowl. Pulse the mixture about 3-4 times until the nuts and butter have been broken down into small pebbly pieces. Set aside. (The streusel with the butter and nuts will be for the top of the cake). If you do not have a food process, you could also do this with a pastry cutter but note it will take a bit more time.
For the Cake - In a small bowl, combine the eggs, 1 cup of the sour cream and vanilla and set aside. In the bowl of a standing mixer, combine the flour, sugar, baking powder, baking soda, and salt at low speed, about 30 seconds. Add the butter and remaining 1/2 cup of sour cream and mix at low speed until the dry ingredients are moistened. Increase to medium speed and beat 30 seconds. Scrape down the sides of the bowl with a rubber spatula. Decrease the mixer speed to low and slowly incorporate the egg mixture in 3 additions, beating for 20 seconds after each and scraping the sides of bowl as necessary. Increase speed to medium-high and beat for 1 minute (the batter should increase in volume and become aerated and pale in color).
Add 2 cups of the batter to the prepared pan. With an offset metal spatula or rubber spatula, smooth the surface of the batter. Sprinkle with 3/4 cup streusel filling (without butter or nuts). Drop 2 more cups of the batter over the streusel and spread evenly. Then add the remaining streusel filling. Top with remaining batter and then the streusel topping (with the butter and nuts).
Bakes until the cake feels firm to the touch and a toothpick comes inserted into the center comes out clean, about 60 minutes. Cool the cake in the pan for about 30 minutes. Then release the clasps of the springform pan and cool completely and serve.