Put the thyme sprigs on a foil-lined baking sheet. Line the bacon strips over the top then sprinkle with brown sugar. Transfer to the middle rack of the oven and bake until crisp, 18 to 20 minutes. Remove from the oven and set aside to cool, then crumble or chop the bacon along with sticky thyme and set aside. In a blender, add the chives, garlic, buttermilk, mayonnaise, lemon juice, lemon zest and hot sauce. Blitz until smooth. Taste, then season with salt and pepper, to taste. Arrange the lettuce on serving platter, drizzle with buttermilk dressing, and sprinkle with crumbled bacon before serving.