Iceberg with Tomatoes, Blue Cheese, and Bacon

Preheat oven to 350 °F. Toast walnuts on a rimmed baking sheet, tossing once, until golden brown, 8 –10 minutes. Let cool; coarsely chop. Cook bacon in a large skillet over medium-high heat, turning halfway through, until brown and crisp, 8 –10 minutes total. Transfer to paper towels to drain. Let cool; crumble. Place half of blue cheese in a medium heatproof bowl and microwave on medium until melted, about 1 minute (this will make it easier to whisk). Add crème fraîche, mayonnaise, vinegar, lemon juice, and hot sauce to blue cheese and whisk until smooth; season dressing with salt and pepper. Cover and chill until cold, at least 30 minutes. Place 1 slice of iceberg lettuce on each plate and spoon about 1/4 cup dressing over each. Top with walnuts, bacon, celery, tomatoes, tarragon, and remaining blue cheese.