Hi vgstephens
I don't regard myself as a pro, but I have made quite a number of potjies in my time.
The secret to a good potjie is
SLOW COOKING. I believe a potjie must stay on the coals for at least 3 hours, but 4-5 hours if you make oxtail or ostrich neck (this, by the way is the ultimate!) You can image that this means low temperature.
Don't put your potjie on the fire as seen in the link above (sorry CC

- you will end up with charcoal). Rather make a fire with the hardest possible wood (gives the longest lasting coal) and put the potjie close to the fire. Put a couple of coals under the potjie and add new coals as the old ones burn out. You must therefore have a small fire going as a source of new coals. That is why a potjie have legs - to get the coals underneath. Elsa is right that it goes directly on the coals, but not the fire.
If you get to baking bread in a potjie you can place a number of coals on the lid to ensure heat from all around.
I prefer to fry my meat brown in the beginning and therefore I will start with a very hot potjie, but after 10 min it should only simmer. If you hear the potjie boiling it is to hot. It should only simmer and you will learn to hear when your potjie is at the right temperature.
There is a lot of steaming going on in a potjie so don't open it for no reason. Don't stir it either otherwise you are making baby food.
In general you put the food in layers and the food that will get ready the fastest will be the top layers (can be added later.) My order for any potjie is as follows: 1) meat browned in onions 2) potatoes 3) carrots 4) other vegetables like sweet potato, cauliflower, etc 5) mushrooms 6) sauce.
It should not be too difficult to find a potjie to buy. You will find that they come in different sizes, but you simply buy one that looks big enough for your family size. Rather buy larger than smaller.
Enjoy, making the potjie and "kuier" while it is simmering, is half the fun.
Hoephoep
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The Creator is bigger than His creation!
My latest trip report to Addo during June 2009:
http://www.sanparks.org/forums/viewtopic.php?f=27&t=34300