Roast the tomatoes at 400°F until softened and caramelized, about 25–30 minutes.
In a blender, combine roasted tomatoes and vinegar; blend until smooth.
Sprinkle in xanthan gum and blend again to thicken slightly.
With the blender running, slowly stream in warm bacon fat until emulsified.
Add mayonnaise, salt, and cayenne; blend until smooth and fully incorporated.
To assemble, layer cabbage on a serving plate. Drizzle with BLT vinaigrette in a zigzag pattern.
Top with butter-toasted sourdough crumbs, tomatoes, and crispy bacon.