GREASE 13x9-inch baking pan.
MIX chocolate, nuts, 2/3 cup of the sugar and cinnamon; set aside. Mix flour, baking soda, baking powder and salt; set aside.
BEAT butter, remaining 1-1/3 cups sugar and vanilla in large bowl with electric mixer on medium speed until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Add flour mixture alternately with sour cream, beating after each addition until smooth. Spoon 1/2 of the batter into prepared pan. Top with 1/2 of the chocolate-nut mixture. Repeat layers.
BAKE at 350°F for 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool in pan on wire rack.
Make-Ahead: Prepare as directed; cool completely. Wrap in plastic wrap, then again in foil. Freeze up to 1 month.