This is a creamy Italian-style sauce that I regularly serve warm, over hot noodles or cold, spread on crackers. The combination of the sour yogurt, tangy garlic and bitter walnuts makes for a nice, balanced sauce. This recipe works best with a yogurt that contains 5% milk fat or higher. Add enough so that the sauce is a bit wetter than you'd like because the dry ingredients will absorb a fair amount of liquid. You don't need to use your best extra virgin olive oil because the food processor will ruin its flavour, pure grade olive oil is fine.