Use the lower 6 inches of 3 stalks of lemongrass, outer leaves discarded and the stalks sliced Into a food processor with the motor running drop the garlic, the lemongrass, and the gingerroot, blending the mixture well, add the turmeric, the lemon juice, and the salt, and blend the mixture, adding the oil if necessary, until it forms a paste, Transfer the paste to a jar with a tight-fitting lid. The paste keeps, covered and chilled, for 2 weeks. Makes about 2/3 cup.