To slice the chilies: cut the top off and slice in half lengthwise. Remove the center veins and all the seeds. If you like it with more heat, leave some seeds in. Slice the chilies in about 1/2 inch pieces. Grind them in a food processor or grind them in a mortar and pestle until they become a thick paste - you may need to add up to 1-2 tablespoons of water to get it going. Pour the paste into a yet unheated wok or sauce pan set on medium to high heat. As the sambal heats up, add the salt and vinegar. Stir well. Leave on medium for about 10 minutes, stirring regularly.

Makes about 1 cup sambal oelek.

source: http://highoverhappy.blogspot.com/2009/09/recipe-sambal-oelek.html