Heat oven to 350°F Spray 12-cup fluted tube cake pan with baking spray with flour.
In large bowl, beat 1 cup butter and the granulated sugar with electric mixer on medium speed until light and fluffy. Beat in eggs, one at a time, until blended. Stir in 1/2 teaspoon vanilla. Stir in flour, baking soda, salt and cinnamon. Stir in apples and walnuts. Spoon into pan.
Bake 50 to 65 minutes or until toothpick inserted in center of cake comes out clean. Cool 10 minutes. Remove from pan to cooling rack. Cool completely, about 1 hour 30 minutes.
In 2-quart saucepan, heat Vt cup butter over medium heat, stirring constantly, until golden brown. Gradually beat in powdered sugar with spoon. Stir in 1 teaspoon vanilla and enough milk until frosting is smooth and desired spreading consistency. Generously spread frosting overtop and partially down side of cake. To serve, cut cake with serrated knife.