Sambal is a condiment or sauce that's highly valued and used daily in Indonesia. It's generally more or less pedis, which means hot as in spicy; that's because the main ingredient is peppers. A good, not too hot base pepper is lombok; rawit peppers are hotter.
If you're not used to eating very hot peppers, use nothing but lombok peppers to make your first sambal. You can always upgrade by adding some rawit or other varieties to a later batch.

There are probably as many sambal recipes as there are Indonesian aunts and grandmothers. This one here is a fairly basic sambal recipe, but not the most basic there is; that would be sambal oelek, which is pretty much ground up lombok peppers and not much else. Boring, right?
So this version uses onions and garlic to add some aroma. And also, the onions help dilute the peppers somewhat, so this sambal is not crazy hot. That makes it suitable for daily use, if you like that kind of thing.
For extra flavour, I've added ginger (djahe); feel free to leave that out if you don't like it. Experiment! Making sambal is easy and fun!

I learned to make this from KKN-Peter at Hack42. Remember kids, brush your teeth, and support your local hackerspace!

Step 1: What You'll Need

Ingredients:

250 grams of peppers (if this is your first sambal, use lombok or a similar run-of-the-mill red pepper)
one or two onions depending on their size. I used red ones, they're slightly more aromatic.
three cloves of garlic
a piece of fresh ginger the size of your thumb
cooking oil (I used coconut and sunflower)
salt

Tools:

good sharp knife and chopping board
garlic press
blender or other food processor
frying pan or wok or wadjan
spatula
clean glass jars with lids

Warning
Word to the wise: if you're a dude, it's smart to wear gloves. You'll know why, the next time you go pee.
Whatever your gender, DO NOT rub your eyes or pick your nose during or right after making sambal.

The best way to get capsaicin (the stuff that makes peppers hot) off your hands is to dissolve it in oil first, then to wash the oil away with soap. Use cooking oil: rub it on your hands before washing them with soap. Memorize this information. You'll thank me later.

Step 2: Get Things Started

Start by chopping your onion(s) very finely, using your tool of choice. It's fine if this is a food processor, but a knife works, too.
I used a Blitzhacker, but you may not have one on hand.

Then put your skillet, frying pan, wok or wadjan on, add a generous amount of oil and heat it on moderate heat. Don't let it get too hot, we're not going to fry anything.

Once it's warm, add your onions. Peel and press three cloves of garlic over them. Let it all simmer gently, don't let the onions turn brown, that will make them bitter. Just let them get soft, sweet and kind of glassy looking. This will take about ten minutes.

Step 3: Now Add Some Heat

Remember those gloves, gentlemen? This is when you put them on.

While the onions are simmering, chop up your peppers. They, too, need to be finely chopped; I used an immersible blender. Add a splash of sunflower oil to make a paste or liquid, not dry-ish pepper flakes.

Once your peppers are all chopped or ground up, add them to the onions and stir. Be careful, you may notice that the capsaicin in the air is enough to make your eyes burn and your nose get runny!

Step 4: Add Extra Flavour

Now peel the ginger, using a sharp knife, and chop it into tiny bits. It's easiest to start by cutting very thin slices and then go from there. Add it to the simmering mixture. Also add about half a (small) teaspoon of salt.
Add some more oil, too; hard to say how much, but don't be stingy. Sambal is greasy in nature. The oil helps conserve the sambal, and also tastes good because capsaicin dissolves in it (remember?)

Stir and simmer some more. And then, it's time to taste.
Be careful! Start with a tiny bit! This is fiery stuff.
Are you happy with the result or does your sambal need anything more? Maybe more salt, maybe a bit of sugar to round off the flavour, lemon juice for a bit of tang, or even some spices like curry powder, cumin or lemon grass? Smell the jars to decide whether their contents would go well with your mixture and improve it. Taste several times, take your time. You could use a cracker or two as a palate cleanser.

Step 5: Final Step

Once you're fully satisfied with your sambal, that means it's done!
Have your glass jars clean and ready, and rinse them with boiling hot water just before filling them. Spoon the hot mixture into them and close the lids immediately. That way, your sambal is sort of sterilised and will keep better.

All done! Share with friends, and enjoy your lovely fiery sambal on cheese, on fish, on a fried egg, with rijsttafel... so many options. But above all, enjoy!