For The Cake, Place A Rack In The Center Of The Oven, And Preheat The Oven To 350°F.
Butter And Flour A 10″ Tube Pan, And Shake Out The Excess Flour.
Set The Pan Aside.
Place The Butter And Brown Sugar In A Large Mixing Bowl, And Beat With An Electric Mixer On Medium Speed Until Light And Fluffy, 3 To 4 Minutes.
Add The Eggs, One At A Time, Beating After Each Addition.
Blend In The Vanilla, And Set The Batter Aside.
Sift Together The Flour, Baking Powder, Baking Soda, Cardamom, And Salt In A Large Mixing Bowl.
Add This To The Batter Alternately With The Sour Cream, Beginning And Ending With The Dry Ingredients.
Don’t Overmix.
Set Aside.
For The Filling, Stir Together The Sugar, Cinnamon, And Walnuts In A Small Bowl.
Spoon A Third Of The Batter Into The Bottom Of The Prepared Pan And Spread The Batter To The Edges.
Scatter Half Of The Filling Over The Top.
Spread Another Third Of The Batter On Top, And Scatter The Remaining Filling Over It.
Spread The Last Third Of The Batter Over The Filling, And Place The Pan In The Oven.
Bake The Cake Until It Has Browned Well On Top And A Long Toothpick Inserted In The Center Comes Out Clean, 60 To 65 Minutes.
Remove The Cake From The Oven, And Place It On A Wire Rack To Cool In The Pan For 20 Minutes.
Run A Knife Around The Edges Of The Pan, Give The Pan A Gentle Shake, And Invert The Cake Once And Then Again So It Cools Completely On The Rack, Right Side Up, About 1 Hour.
Slice And Serve.
