Roasting oysters, such as the way they are prepared at Bowens, is not the way I prefer.
I'm going to show you the best way, developed over years of cooking oysters for small and large groups of people.
First, the oysters.
If you have oysters on the shell available to you, than this is the preferred method.
Steamed Oysters in their Shell
We buy our oysters by the box at a local grocery store, with 100 to a box. This is about the same as a bushel of oysters, which is how I bought them when I was younger, but stores don't seem to carry them this way now.
I take the number of people that are going to eat oysters, and divide by 6, and that's the number of boxes of 100 I buy. Since I can't buy a part of a box, I round up to the next box. So for 20 people that are going to eat a meal of oysters (not talking about those people that either don't like them, or not had them, but people that know they like oysters and know they want a full meal of them), I'll end up with 3.3 boxes, rounded up to 4 boxes, or 400 oysters.
For 20 people, you will need 5 turkey fryers (burners) in order to keep the people supplied with oysters in a constant flow. This is going to be a lot of work for the main oyster cook! These are the propane cookers with stand, a lift out boiling pot, and a metal pot. It's probably about 5 gallons.
We pour all 400 oysters into a hard-plastic pond liner (about 20 gallons) and cover with ice. We take them out one-at-a-time wearing water proof kitchen cleaner gloves, inspecting each one before it goes into the boiling pot.
Place about 3 inches of water in the bottom of the pot. Bring it to a boil. Do this for all the burners you have, as some oysters will have died and their shell will be open; you don't want to serve these. Use an oyster knife to pull the lid off of these or discard the whole oyster if not in a cluster.
Fill up, about 3/4 full, the boil pot (the one with the holes in it), and lower it down into the boiling pot. The water in the pot should be below the level of the oyster boil pot; if it's too high, then use a ladle to remove some. You'll be removing water from the pot all night, so you'll need a long handled ladle for this task.
Put the lid on, and kick up the burner to high. It will be making a roaring noise. You'll need to do this because the cold oysters will take a lot of heat out of the pot.
When steam starts coming out of the top of the lid, take a look. If there's just wisps of steam, you are too early - you want a cloud of steam rising up and through the oysters, indicating that all of the oysters have been heated enough to be cooked.
I like to leave mine in the pot until a froth bubbles up, but you'll need to experiment with this.
Do it this way, you'll be able to cook the oysters at a much more precise, lower temperature, than that used in roasting. For this reason, you don't have to be as precise as to the time to cook, they are harder to over cook, and all will come out at the same temperature. Plus, the steam helps clean everything!
Oysters from a Pint Container
Depending on where you live, you may not be able to obtain oysters in the shell (not the half-shell; that's a serving of raw oysters that have had their lid removed). However, you may be able to find, if your grocery has a 'seafood' or 'fish' section, oysters that have been shucked and placed into a pint container. I'm not talking about oysters in a tin can or sardine-like container. You should be able to see the shucked oysters through the clear pint container, in their liquid.
At home, depending on how many people you are serving, get a large pan, and pour all of the oyster liquid into it. You'll want the liquid in the pan to come up about 1/4 inch, or about half way up an oyster. It doesn't really matter if you have more water, it just will take longer to bring it up to temperature. You don't want less water then would come up half way on the oyster.
Bring the water up to a simmer, then immerse your oysters into it carefully so you don't splash hot water out of the pan. You'll want a pan big enough so you can serve one serving to everyone at the same time. If you have more people, either add more pans, or cycle between people. You want to serve a small serving to everyone, so everyone will eat their oysters hot before they have had a chance to cool down.
So you'll be cooking many servings. When its just the two of us, I'll cook the pint in 2 or 3 separate servings, so they are all hot.
Serve with Tobasco, Texas Pete, or your favorite condiment.
We usually don't put anything on them.