Preheat oven to 350°F Grease and flour 9-inch round pan.
Mix together flour, cinnamon, baking powder, and salt.
Beat together butter and sugar at medium speed until light and fluffy. Add eggs, one at a time, beating well after each. At low speed, alternately beat flour mixture and milk into butter mixture. Stir in carrots and nuts. Pour into prepared pan.
Bake cake until top springs back when lightly touched, about 40 minutes. Cool in pan on wire rack for 10 minutes. Turn cake out onto rack to cool completely.
To prepare icing, beat together butter and cream cheese at medium speed until smooth. Beat in vanilla. Beat in confectioner's sugar until well blended.
To prepare topping, mix together nuts and brown sugar.
Place cake on serving plate. Spread icing over top and sides. Sprinkle with nut mixture.