Nothing needs to be too exact with this. The core ingredients are fresh whole red chillies and salt. You could also add some of garlic, dried chilli flakes, cumin seeds, fish sauce, palm sugar and/or vinegar. Remember sugar and vinegar tend to balance the salt content of foods. My favourite goes something like this:
A handful of fresh hot red chillies (whole)
A few cloves of garlic (whole)
1/8th teaspoon cumin seeds (watch it they are pretty powerful, less rather than more)
½ teaspoon salt (more or less)
Put all ingredients in a mortar and pestle and crush until you have a paste. Transfer to jar and pore a thin layer of olive oil to cover surface. Try not to eat it on toast for breakfast. If you start the day like this, you’ll go through your sambal pretty quickly! Does go well with eggs though.
Note: The seeds in chillies contribute to their heat. If you want the paste to have less heat, either remove seeds or (obviously) use milder chillies.