4 large plum tomatoes, bottoms marked with an X
1/4 C. extra-virgin olive oil
1 tsp. finely chopped thyme
Salt and freshly ground pepper
2 ounces brioche, cut into 3/4-inch cubes (2 C.)
1/3 C. mayonnaise
1/4 C. crème fraîche or sour cream
1/4 C. buttermilk
2 1/2 T. fresh lemon juice
1 T. chopped flat-leaf parsley
1 1/2 tsp. chopped mint
3 T. snipped chives
1/2 pound thickly sliced bacon, cut into 2-by-1/2-inch pieces (or lardons if you can find unsliced bacon)
2 medium heads of iceberg lettuce, cut into 4 wedges each

Preheat the oven to 275°. Prepare a bowl of ice water. In a medium pot of boiling water, blanch the tomatoes just until the skins loosen, about 30 seconds. Using a slotted spoon, transfer the tomatoes to the ice water to cool. Drain and peel the tomatoes, pat dry and halve crosswise. Arrange the tomatoes, cut side up, on a nonstick baking sheet and drizzle with 2 T. of the olive oil. Sprinkle with the chopped thyme and season with salt and pepper. Roast for about 2 1/2 hours, or until the tomatoes are very tender and slightly shrunken. Transfer the tomatoes to a plate and let cool. Meanwhile, spread the brioche cubes on a small baking sheet and toast for about 15 minutes, or until golden and crisp. Let the croutons cool. In a small bowl, whisk the mayonnaise, crème fraîche and buttermilk until smooth. Add the lemon juice, parsley, mint and 1 T. of the chives and season with salt and pepper. Refrigerate until chilled. In a medium skillet, cook the bacon over moderate heat, stirring occasionally, until browned and slightly crisp, 8 to 10 minutes. Transfer to paper towels to drain. Put each iceberg wedge on a plate, add a tomato half and drizzle with the remaining 2 T. of olive oil. Scatter the croutons and bacon on top. Garnish with the remaining 2 T. of chives and serve, passing the buttermilk dressing at the table.