How to Make It
In a medium bowl, whisk the buttermilk with the sour cream, shallot and cider vinegar. Stir in the blue cheese. Season the dressing with salt and pepper.
In a large nonstick skillet, cook the bacon over moderate heat until crisp, about 6 minutes. Using a slotted spoon, transfer the bacon to paper towels to drain.
In a very large bowl, toss the spinach with the red onion and bacon, then toss with the dressing. Mound the salad on plates, top with the eggs and serve.