Like many of you, I brew beer on my kitchen stove. I do have a Banjo Burner, and it does kick butt, but it's just not practical during the winter months. The unfortunate downside to brewing indoors is that my electric stove burners aren't powerful enough to do a full-volume boil. Back when I had a gas stove, I could put a 10 gallon Megapot across two burners and get a decent rolling boil. But the electric stove just can't quite make it. Instead of scaling down my batch size, though, I use two medium-sized pots and split a 5 gallon batch of wort between them. It's called the Texas Two-Step or Split Boil method.
Why bother with a full-volume boil? Well, a partial volume boil, where a condensed wort is boiled and then diluted with water after cooling, has three distinct disadvantages. First, boiling a condensed wort leads to more browning in the kettle and a darker finished product. Not a big deal for a stout, but a pilsner or cream ale needs that light color to be true to style. Secondly, the hop utilization is less efficient in a condensed wort. If you are trying to brew something that needs a lot of bitterness, like a Double IPA, it can be pretty tough without a full-volume boil. The last big factor is all-grain brewing. If you want to brew all-grain, a full volume boil is pretty much necessary.
One of the main proponents of the Texas Two-Step method is Chris Colby over at Brew Your Own Magazine. In Chris' description, the brewer would completely boil one half of the wort, cool it, and add it to the fermentor before starting the boil on the second. Some folks even suggest brewing the second half the following day and adding it to the already-fermenting first half.
The method I use is perhaps more accurately described as a split boil, but the same concepts are involved. I've got a couple of pots that are larger than 3 gallons each, so I can split the batch between the two of them and boil both simultaneously. I use the 5 gallon kettle that I started out using in extract brewing for about 1/2 of the wort and an 8 gallon Megapot for the other half. You could use just two 5 gallon kettles, though. The evaporation rate is higher when you have two kettles going instead of just one, so I shoot for at least 6.5 gallons of wort pre-boil to get 5 gallons in the fermentor, instead of my normal 6 gallons. If you get a vigorous boil on your stove with 3-4 gallons of liquid, you'll want to increase that to 7 gallons or so.
Once the kettles are at a boil, I simply split the hop additions between the two kettles. For hop utilization rates, it shouldn't matter much if one kettle has the high gravity first-runnings and the other has a lower gravity, or if both have the same gravity (it is a bit different, but pretty darn close). But if you were to have one kettle of the first runnings and another of the last runnings, they would have different pH, and I've read that a pH that is way off can result in the extraction of more astringent flavors from hops. So to keep things even, I pull the wort into a single vessel and mix before splitting it into the two pots. A 6.5 Gallon Bucket with spigot would work well for this purpose. If brewing extract, you could just split the extract/sugar additions between the two kettles.
A final consideration is chilling - if it takes you 20 minutes to chill down 3 gallons of wort, you might not want to just wait on one pot while chilling the other. Any late addition hops might loose some of their aroma/flavor potency in the kettle with hot wort in it. Ideally you want to chill all the wort down quickly. One method would be to prepare an ice bath for one pot and use a wort chiller on the other. If you are obsessive about water use like I am, you can use the waste water from the wort chiller to fill up a lukewarm bath for the other kettle, which should take the temperature down enough to preserve hop aroma. Then you can switch the chiller to the other kettle to take it down the last ~30 degrees or so. It might seem like a good idea to combine the wort before chilling, but the splashing during transfer would result in hot side aeration that might be detrimental to the final product.
Hopefully this will help some people keep brewing all-grain during the winter (or rainy days) and others who don't want to invest in a huge kettle for full volume boils. Cheers!