This recipe will create a category box for each of your top categories that have subcategories. To cover top categories that have products right in the next level without subcategories, a top navigation bar is added.
Your navigation will look like the following screenshot, with top categories added in a bar at the very top of the page:
Note
Chef's suggestion:
If your setup has five top categories with active subcategories and two top categories with products right on the first level, your infobox headers will show all seven top categories in the left column, but only five category boxes will show with subcategories obviously; the top categories that have no subcategories will show as links that direct to their product listing. See the Chef's suggestion below (at the end of the Cooking section) for a hack that only shows the box if there are subcategories for this top category.
Go grab your cookie cutters, and have fun hacking your...