There are dozens of regional sambal variations across Malaysia and Indonesia. This guide focuses on the two most useful for home cooking: sambal belacan, a raw condiment served at the table, and sambal tumis, the cooked version that goes into nasi lemak, stir-fries, and dozens of other dishes. They share some ingredients but are built differently and used differently.
The simplest sambal. Pounded rather than cooked. Sharp, spicy, and sour - eaten in small amounts alongside rice, grilled fish, and vegetables.
Pound chilies and belacan in a mortar until broken down but still slightly chunky - this is not a smooth paste. Add lime juice, sugar, and salt. Taste: it should be spicy, tangy, salty, and slightly sweet. Serve immediately or refrigerate for up to 3 days.
This is the batch-cook sambal that goes into nasi lemak, fried rice, noodles, and eggs. More complex than sambal belacan, with more depth and sweetness, and it keeps much longer.
For this quantity of dried chilies, the sambal will be moderately hot. To reduce heat: remove the seeds from the soaked chilies before blending, or swap some dried chilies for dried ancho/guajillo which are milder. To increase heat: add 2-3 bird's eye chilies to the blend.
Sambal tumis is the base for nasi lemak's condiment - serve 1-2 tbsp per person alongside the rice. It's also the starting sauce for many stir-fries: fry 2-3 tbsp sambal in hot oil, add protein and vegetables, season and serve. Use it as a flavouring for fried rice instead of chilli sauce. Stir into coconut milk for a quick curry base. Once you have a jar in the fridge, it becomes the answer to "what should I cook tonight?"
Sambal is the most versatile ingredient in Malaysian cooking. For the broader context of how it fits into dishes like nasi lemak, nasi goreng, and laksa, see the Malaysian home cooking guide.