Step 1

Put vegetable oil in a large, heavy saucepan. Heat over medium heat and then add chilies and onion. Saute over low heat for about 10 minutes, stirring regularly.

Step 2

Add garlic and saute for 5 minutes until everything is very soft, being careful to make sure it doesn't take on any color.

Step 3

Put the contents of the saucepan into a food processor or blender and blitz until smooth. Store in the fridge in a sterilized jar.