Walnuts give this easy, no-cook sauce an amazing richness and depth of flavor, along with a creamy consistency. Herbs add color and freshness, while capers and lemon zest and juice balance with tangy brightness. Though the ingredients are blitzed in a food processor, roughly chopping them first ensures they readily break down. Spoon this pesto-like sauce onto seared or grilled steak or fish or even on roasted vegetables. It also makes a great spread for crostini or sandwiches.