I'm trying to think how to explain hoppers. First, you need an odd pan to make them - a half hemisphere of iron, much more curved than a wok. You can buy them in Indian grocery stores (or they can tell you where to get one). If you buy one, you have to remember to dry it right away after you wash it, and then rub oil on the inside, or it will rust. (El reminded me of that). Once you have the pan, you rub it with an oily paper towel (or fry nonstick cooking spray on the inside), and heat it a little. Then you pour in a half cup of batter, right into the bottom. Then you pick up the pan and swirl it a bit, so that a thin layer of batter comes halfway up the sides of the pan, and the rest settles back down at the bottom. For a plain hopper, you stop there, and put a lid on the pan (any lid that fits just inside the rim is fine) and cook it for five minutes on low heat. A very slow process, as you see. To feed four people would take an hour (two hoppers a person is more than sufficient; they're substantial). It's good for lazy mornings when you can just relax and chat in between each hopper's cooking, or do dishes, or putter around the kitchen.
There are variations on the plain hopper (which is traditionally eaten plain, or with curry). For something more Americans would recognize as breakfast, you crack an egg into the center right after you swirl. It settles in and in five minutes has soft-cooked; traditionally, you'd eat it with the yolks still somewhat liquid. I'm not a big fan of liquid yolks, but it works with this dish. Kids are often really fond of a sweet hopper, where you add a quarter cup or so of sweetened coconut milk to the center after you swirl, and serve with more coconut cream. Not a low-fat meal, but yummy.
The batter is somewhat complicated, though not actually hard. Add a packet of yeast to a half cup of warm water and a quarter t. sugar. Wait ten minutes and see if it bubbles. If it doesn't, your yeast isn't active. Start over. When you have active yeast, mix together 1.5 c. flour, 1.5 c. ground rice (you can grind it in a coffee grinder if you don't have a spice grinder), and 1-2 t. salt (err on the lower side to start). Take a can of coconut milk (two cups). Pour 1.5 c. into the flour mixture. Dilute the other half cup with a half cut water and set the cup of thin coconut milk aside. Stir in yeast, blend very well, and set aside, covered, ideally overnight (or for an hour in a warm oven with the heat turned off).
When it's done rising (theoeretically it should double in bulk, but I wouldn't count on it), stir it again, stirring in half of the thin coconut milk. It should be a medium thick batter -- thin enough that when you pour it and swirl, you leave a thin layer on the sides of the pan. It's pretty easy to get the hang of after the first couple (much like crepes).
I don't know how to describe the taste of hoppers. More like injera than anything else I suppose, but not as sourdough-ish. For a seriously Sri Lankan feast, serve them with a good hot curry (fish is best), make some egg, some sweet, serve some idli and masala dosai and sambar, put out some sharp sambols and sour pickles and sweet hot chutneys, with lassi and king coconut milk to drink and fresh fruit (mango, papaya, pineapple) on the side. That breakfast will carry you through to dinner. I'm not even going to start describing dinner, or I'll get hungry again, and I just ate two hoppers, so I'm really quite full.