Preheat oven to 350. Grease 9" round cake pan. Dust with flour; tap out excess.
Mix together flour, cinnamon, baking powder & salt. Beat together butter & sugar at medium speed until light & fluffy. Add eggs, 1 at a time, beating well after each. At low speed, alternately beat flour mixture & milk into butter mixture. Stir in carrots & nuts. Pour batter into prepared pan. Bake cake until top springs back when lightly touched & a toothpick inserted in center comes out clean, about 40 min. Transfer pan to wire rack to cool for 10 min. Turn cake out onto rack to cool completely. Prepare icing: Beat together butter & cream cheese at med speed until completely smooth. Beat in vanilla. Beat in confectioners sugar until well blended. To prepare topping, mix together nuts & brown sugar. Place cake on serving plate. Spread icing over top & sides. Sprinkle with nut topping mixture.