For the Pickled Raisins: In a small saucepan, combine vinegar, water, sugar, salt, and mustard seeds, if using, and bring to a boil over medium-high heat. Cook, whisking occasionally, until sugar is dissolved, about 1 minute. Remove from heat.
In a medium bowl, combine raisins and hot vinegar mixture. Allow raisins to cool to room temperature, uncovered, about 30 minutes. Transfer raisins to airtight container and refrigerate for at least 1 hour or up to 1 month.
For the Dressing: While raisins cool, in a small bowl, whisk together crème fraîche or sour cream, mayonnaise, sugar, vinegar, and salt; set aside.
For the Salad: In a large bowl, combine broccoli, bacon, apples, cheese, sunflower seeds, and almonds. Add reserved dressing and toss to coat evenly. Cover and refrigerate until chilled, at least 1 hour or up to 24 hours.
When ready to serve, drain raisins with a fine-mesh strainer, and toss with broccoli salad until well incorporated. Serve.
