1. Preheat oven to 350°.
2. In a medium mixing bowl, beat 3 tbsp. butter with brown sugar and cinnamon until a coarse, sandy mixture forms. Stir in chocolate chips and nuts; set aside.
3. In another medium mixing bowl, whisk together eggs, 1 cup sour cream, orange juice, zest and vanilla; set aside.
4. In an electric stand mixer, mix flour, sugar, baking powder, soda and salt.
5. Using a paddle attachment, beat in remaining butter and sour cream a little at a time until a coarse, wet, sandy mixture forms.
6. Add egg mixture in 3 additions, beating on low until fully incorporated.
7. Increase speed to medium-high; beat for 2 min.
8. Lightly spray a 9" square nonstick baking pan with cooking spray; line bottom only with parchment paper.
9. Pour ½ of the batter into bottom of pan; sprinkle ½ of the nut mixture over batter.
10. Pour remaining batter evenly over top; sprinkle with remaining nut mixture.
11. Bake in preheated oven for 1 hr., tenting pan loosely with foil in the last 30 min. of baking, if needed, to control excess browning.
12. Remove from oven; let cool completely in the pan on a wire rack.

Tasty Tip:

• Cake may be frozen, tightly wrapped, for at least 3 months. Thaw in the wrapping for best results.