Streusel
1 1/2 cups brown sugar
1 tablespoon cinnamon
6 tablespoons chilled butter, diced
1 1/2 cups coarsely chopped pecans
1 cup semi-sweet chocolate chips
Cake
3 cups flour
1 1/2 teaspoons baking soda
1 1/2 teaspoons baking powder
1 1/3 cups sugar
3/4 cup softened butter
3 eggs
1 1/2 teaspoons grated orange peel
1 1/2 teaspoons vanilla extract
1 1/2 cups sour cream
1/4 cup orange juice

Streusel
Whisk together brown sugar and cinnamon. Add butter and rub in with fingertips till mixture holds together in small, moist clumps. Mix in pecans and chips. Mixture can be covered and held in refrigerator up to 3 days.
Cake
Heat oven to 350°F. Butter and flour 9x13 inch baking pan. Sift dry ingredients together. Cream together sugar and butter till smooth. Beat in eggs one at a time. Add vanilla and peel. Mix in dry ingredients alternately with sour cream in 4 additions, beginning and ending with dry. Mix in juice. Spread half of batter in prepared pan. Sprinkle with half of streusel. Drop remaining batter over by heaping tablespoonfuls and spread carefully to make even layer. Sprinkle with remaining streusel. Bake 30 minutes. Lay sheet of foil on top to prevent overbrowning and continue baking (recipe cuts off here) till toothpick inserted in center comes out clean.

This will need to be tested to determine a final cooking time.