Yes, you can.

When setting up the menu item, in the 'Manage Menu Items' page under 'Manage Your Menu', you will find a dropdown box asking whether the item is limited in number or not. If you only have a certain number to sell, select 'Yes' and enter the number of items available.

As the item are purchased, the number available will decrease. Once the number hits 0, the item will be taken off the menu - the 'Currently Available' flag will be set to 'No'.

You can check the number of items remaining at any time in the table in the 'Manage Menu Items' page. You can also change the amount manually by selecting 'Edit' in that table, entering a new number and clicking on 'Update Menu Item'.