In a large skillet over medium heat, add chopped crispy bacon and fry for about 8–10 minutes until golden brown and crispy. Transfer to a paper towel-lined plate, reserving about 3 tablespoons of bacon grease in the skillet.

In the same skillet, add thinly sliced onions and sauté over medium-low heat for approximately 10–12 minutes until golden and tender.

In a mixing bowl, combine the warm bacon grease with honey and Dijon mustard, whisking until smooth. Adjust sweetness or acidity as needed.

In a large serving bowl, layer fresh spinach, add warm caramelized onions, crispy bacon pieces, and sliced hard-boiled eggs. Gently mix to ensure even distribution.

Drizzle the hot bacon-honey mustard dressing over the salad, toss gently to combine, and serve immediately.