There are three upgrades for the cauldron that I know of. You have the spice rack, as described above, the pots and pans, and the butcher's table. You need iron for those, though. There are a number of new recipes you can make in the cauldron once you have iron and turnips. Some that used to be in the cauldron, like Bread and Lox Meat Pie, have been moved to the oven. You make them in the cauldron, then bake them in the oven before you can use them. Enjoy!