- Nonstick vegetable oil spray
- 2 large egg whites (1/4 cup)
- 1/3 cup (packed) golden brown sugar
- 1 1/2 cups coarsely chopped walnuts
- 1 1/4 cups mini semisweet chocolate chips, divided
- 1/4 teaspoon baking powder
- 1 cup plus 2 tablespoons sugar
- 1/2 cup (1 stick) unsalted butter, room temperature
Position rack in center of oven and preheat to 350°F. Butter and flour 10-inch-diameter tube pan, then spray with nonstick spray. Mix egg whites, brown sugar, and salt in bowl. Mix in walnuts and 1/4 cup chocolate chips.
Whisk flour, salt, baking powder, and baking soda in medium bowl. Using electric mixer, beat sugar and butter in large bowl to blend. Beat in eggs 1 at a time. Stir in flour mixture in 4 additions alternately with sour cream in 3 additions, beginning and ending with flour mixture. Stir in 1 cup chocolate chips.
Transfer batter to pan; smooth top. Spoon walnut mixture evenly over. Bake cake until tester inserted near center comes out clean, about 1 hour. Cool in pan on rack 10 minutes. Turn cake out onto rack; invert onto second rack (walnuts should be on top). Cool. DO AHEAD Can be made 1 day ahead. Wrap in plastic.
Mix powdered sugar and sour cream in bowl; drizzle over cake.