Cook the bacon in a 12" frying pan on top of the stove until crispy.
Put the spinach in a serving bowl and set aside.
With a slotted spoon, remove the bacon from pan and drain on paper towels. Leave 2 Tablespoons of bacon fat in the pan and add 2 Tablespoons of olive oil.
With the burner on medium, heat the oil, then add the mushrooms and shallots. Stir to coat, and cook until the mushrooms are tender and cooked through.
Remove from heat and stir in the balsamic vinegar.
Pour the warm dressing over the spinach, crumble the bacon into the salad, then toss. Add the black pepper to your taste. Salt should not be needed because of the saltiness the bacon and bacon fat lend to the dish.
If using, lay the egg quarters on top of the salad.
Gr8 Do Ahead Tip:The dressing can be cooked through Step 4, then set aside. When ready to serve, reheat the dressing over medium-low heat. Proceed with the balsamic vinegar and the remaining steps.This nutritional information is only an estimate. We do not guarantee the accuracy of the nutritional information for any recipe on this site.