Grease a 9" x 5" x 3" loafpan; line with wax paper. Grease and flour wax paper. Set aside.
Beat butter at medium speed of an electric mixer until creamy; gradually add brown sugar, beating well. Add eggs, one at a time, beating after each addition.
Combine flour, baking powder, and salt; add to butter mixture, beating at low speed until blended. Fold in white chocolate and remaining ingredients. (Batter will be very chunky and thick.)
Spoon batter into prepared pan. Bake at 300° for 1 hour and 15 minutes. Run a sharp knife around edge of pan to loosen fruitcake; cool in pan on a wire rack 30 minutes. Remove cake from pan; peel off wax paper. Cool completely on wire rack.