- Soften butter.
- Preheat oven to 350°F.
- Grease a 9 by 13 baking dish.
- With an electric mixer on low speed, beat the butter and 1 1/2 cups sugar.
- Increase speed to high and beat until fluffy.
- Add flour, sour cream, baking soda, baking powder, vanilla, orange zest, and eggs, and beat on low to medium until well blended.
- Spread half of the batter in the baking dish.
- Chop walnuts and combine with cocoa, cinnamon, and 1/4 cup sugar.
- Sprinkle over batter, and top with remaining batter.
- Bake until a toothpick inserted in the center comes out clean, about 40-45 minutes.
- After removing from oven, sprinkle chocolate chips over the surface of the cake.