How to Simmer
Simmering is a very interesting technique and there's more to it than most people realize. Like many other techniques, have a thermometer ready when simmering.
Simmering a pot of water at sea-level is easy, simply heat the water until small bubbles begin to form on the bottom of the pot and rise to the surface, lower the heat and keep the water looking like that. However, once you start adding in different types of liquids, salts, starches such as rice and oatmeal and anything else you're supposed to simmer, things get a bit dicey.
All that stuff you put in the water will change not only the boiling point of the water, and thus the temperature at which the bubbles form, but it also can impead the bubbles rise to the surface. If the bubbles can't rise quickly enough the liquid will begin to circulate its heat very slowly, thus causing cooling on top and full boiling on bottom, ruining the dish. This is why some foods require you to 'stir constantly for ten minutes', and who wants to do that, not me.
So, if you have a pot of sauce that won't get ruined by some temperature variations then stove-top simmering works just fine. However, if you're looking to simmer more solid food items in a liquid, such as fish or rice, you might want to rethink your simmering technique and try the oven.
Using the oven will allow heat to be applied from all sides of the pot, this will prevent the need to stir all the time as you won't have a build-up of heat on one side as you would get from stove-top cooking.
250°F is a good temperature to keep the oven for a nice simmer for most foods, however if your cooking something starchy like rice you might want to crank the heat up to 325°F - 350°F.
For items such as rice that require the water to be boiled then reduced to a simmer you can take care of that on the stove-top then move the whole pot into the preheated oven.
