Preheat oven to 350 degrees F. Butter 10" diameter by 4" deep angel food cake pan; dust with flour. Mix 1/2 cup sugar, walnuts, cinnamon and cocoa in small bowl. Sift flour, baking powder and salt into medium bowl. Beat butter in large bowl until smooth. Gradually beat in remaining 1-1/4 cup sugar. Beat in eggs 1 at a time, then vanilla. Mix in dry ingredients in 3 additions alternately with milk in 2 additions.

 

Spoon 1/3 of batter into prepared pan. Sprinkle with half of walnut mixture. Top with half of remaining batter, then remaining walnut mixture and remaining batter. Using knife, cut through batter to swirl walnut mixture. Bake cake until tester inserted near center comes out clean, about 55 minutes.

 

Cool cake in pan on rack (can be made 1 day ahead. Cover pan with foil; store at room temperature). Cut around pan sides and center tube to loosen cake. Turn cake out; transfer cake, rounded side up, to plate.