Combine first 4 ingredients in a large bowl; cover with a damp paper towel, and chill.
Cook bacon in a medium skillet over medium heat 5 minutes or until crisp. Remove with a slotted spoon, and drain on paper towels, reserving 2 Tbsp. drippings.
Sauté shallot in 1 Tbsp. reserved hot drippings over medium heat 1 to 2 minutes or until lightly browned. Remove from heat, and stir in vinegar and mustard. Add oil in a slow, steady stream, whisking constantly until smooth. Add salt and pepper to taste. Transfer to a small bowl. Wipe skillet clean.
Cook mushrooms in skillet in remaining 1 Tbsp. reserved hot drippings over medium-high heat, stirring occasionally, 5 to 7 minutes or until tender. Sprinkle with a pinch of kosher salt.
Toss endive mixture with 1/4 cup vinaigrette, and divide among 6 salad plates. Top with eggs, mushrooms, bacon, and bread slices. Serve with remaining vinaigrette.
I made 1/3 recipe but accidentally used 1 T. mustard instead 2/3 t. and loved the results. Although I used this as an entree salad, I think it would be a wonderful starter salad and like this better than many other spinach salads I've tried. This goes into my regular repertoire. Do try it.
I made 1/3 this recipe for two of us for a 'diet' dinner. It was actually very good. I used spring mix for the greens and added the chives to the dressing. The eggs were more than medium and I only let them sit 5 minutes. This would make a nice light luncheon entree.