This versatile Creamy Mustard Sauce offers a lighter alternative to heavy cream-based reductions without sacrificing richness or flavor. By blending nonfat yogurt and sour cream with sharp Dijon and spicy brown mustard, you achieve a velvety texture that coats food beautifully. The addition of red wine vinegar provides a bright acidity that cuts through the fat, while dried marjoram and minced garlic add aromatic depth. It is incredibly quick to prepare, requiring no cooking time, making it an ideal last-minute addition to weeknight dinners. Drizzle it over grilled chicken, pork chops, or roasted asparagus for an instant flavor boost. The sauce can be made ahead and chilled, allowing the flavors to meld even further before serving.