For the soup, heat a large Dutch oven over medium heat and melt butter. Fill pot with onions, bay, thyme, salt, pepper and garlic. Place a lid over half of the pot and sweat onions until deeply caramel and soft, 35-40 minutes, stirring occasionally. Add consommé or demi-glace and water, and dissolve. Add stock or broth, bring to simmer and cook for 30 minutes at a low simmer.
While the soup is simmering, preheat oven to 400°F and bake 8 slices on a slotted pan or wire rack set on a baking sheet to crisp, 12-15 minutes. Remove, raise heat to broil for bread.
Place eggs in a medium saucepot, fill with water and bring to a boil. Remove from heat and let stand for 10 minutes. Cold-shock the eggs, peel and cut into quarters lengthwise.
For the croutons, line a baking sheet with parchment paper and toast bread under broiler on a rack in the center of the oven until light golden. Raise rack 1 notch and cover rounds with cheeses. Broil to brown and bubbly.
Mince remaining slice of bacon, add to a skillet and render over medium-high heat for 2 minutes while stirring. Add shallots and garlic, and stir 3 minutes more. Stir in sugar, black pepper and Dijon, then whisk in vinegar and EVOO. Remove pan from heat and add spinach in bunches, wilting it a bit but keeping it tender-crisp. Toss in mushrooms and onions and top with blue cheese crumbles and eggs.
Serve soup in crock-shaped bowls topped with croutons, with the spinach salad alongside or in separate shallow dishes.MORE
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