How to Make It
In a small saucepan, combine the mustard seeds and vinegar and bring to a boil. Remove the saucepan from the heat and let stand for 1 hour.
Preheat the oven to 450°. In a small ovenproof skillet or baking dish, toss the tomatoes with 1 tablespoon of the oil. Roast for 30 minutes, until the tomatoes have popped and are browned in spots. Transfer to a blender. Add the remaining ingredients; puree until smooth.
In a small skillet, cook the bacon over moderate heat until browned and crisp, 5 to 7 minutes. Transfer to paper towels to drain. In a small bowl, blend the blue cheese with the crème fraîche until smooth. Dollop the mixture onto plates and spread slightly. In a large bowl, toss the lettuce with half of the dressing and season with salt and pepper. Arrange the lettuce on top of the blue cheese mixture. Garnish with the pickled mustard seeds, bacon and chives. Serve the remaining dressing on the side.