Pulse sugars, nuts, cinnamon in food processor until nuts are coarsely chopped. Reserve 3/4 cup to use for filling. Add flour, butter, & vanilla to remainder of batter and pulse briefly to form a coarse, crumbly mixture.
Line a 9″ greased, spring form pan with parchment and then grease again and flour surface. Preheat oven to 350*
In a medium bowl, combine yolks, 1/4 of the sour cream & vanilla
In a large mixing bowl combine the dry ingredients and mix on low for 30 minutes. Add butter and remainder of sour cream. Mix until dry ingredients are moist. Increase to medium speed and beat for 1 1/2 minutes. Scrape down the sides. Add egg mixture in 3 batches.
Reserve about 1/3 of batter and scrape remainder into prepared pan. Sprinkle with streusel filling. Drop reserved batter an spread evenly with spatula. Sprinkle with remaining streusel.
Bake 55-60 minutes until a wooden cake tester inserted in center comes out clean. Let cool.