Combine brown sugar,oil, and eggs, stirring until smooth. Sift together baking soda, cinnamon, nutmeg, salt, cocoa powder, and flour. Beat dry ingredients into liquid, mixing well. Fold in carrots and walnuts. Pour batter into prepared pan and bake for 45 to 50 minutes or until a cake tester inserted near center of ring comes out clean.
Cool in pan on rack for 15 minutes. Turn out cake and let cool completly.
Melt white chocolate in the top half of a double boiler or in a microwave and pour over top of cooled cake.
If desired, garnish with melted dark chocolate driizzled over cake and fresh fruit such as strawberries.