2. Add the walnuts and garlic to the food processor or mortar. If using a processor, pulse on and off to form a coarse meal. Slowly drizzle in olive oil, lemon juice, and vinegar, alternating between each, and continue puréeing until mixture is smooth, but grainy. Season with salt and pepper and stir. If using a mortar and pestle, pound the garlic and a little salt in the mortar with the pestle and add the bread and walnuts. Continue pounding, drizzling in the olive oil, lemon juice and vinegar to form a thick, mealy paste. Serve either at room temperature or chilled.