For an extra touch of sophistication, consider using a piping bag to apply the crème fraîche mixture to the crackers. If crème fraîche is unavailable, sour cream makes an excellent substitute. For a lighter option, try Greek yogurt. These bites are best served immediately to maintain the crispness of the crackers. Experiment with different types of mustard, such as a honey mustard or a spicy brown mustard, to customize the flavor profile. Add a tiny drizzle of high-quality olive oil for extra richness.