With the metal blade in the work bowl of the food processor, process the lemon peel with the sugar until the sugar is colored yellow and there are no large pieces of peel. Remove the lemon/sugar to a small bowl. Add the carrots to the workbowl, and shred with a few long pulses. Remove the carrots to a small bowl. Return the lemon/sugar to the processor, and add the butter or oil, the eggs, and the vanilla. Add the nuts, and pulse on and off two times. Add the flour, baking powder, soda, salt, cinnamon, mace, and nutmeg. Pulse on and off until the flour just disappears. Scrape down the sides of the bowl with a rubber scraper. Add the carrots, and pulse on and off until the shreds disappear. Put the batter into the prepared pan, and bake for 55-60 minutes, or until a toothpick inserted in the middle of the cake comes clean.
Carrot cake stays fresh for up to 5 days. It's a good dessert to serve after a heavy meal because it doesn't feel as rich as chocolate. If you want to make it particularly pretty, dust the top with confectioner's sugar before serving.