Preheat oven to 325F.
Place a medium pot over medium heat and melt the butter. Add the blue cheese to the pan and stir to melt the cheese. Add the cubed bread to the pot and stir to evenly coat. Toss the croutons onto a baking sheet and bake until toasted, 15-20 minutes.
While the croutons are baking, pour the beef stock into a medium saucepot and place over medium heat. Bring up to a simmer and keep warm.
When the croutons are almost done, place a large skillet over medium-high heat with 1 turn of the pan of EVOO, about 1 tablespoon. Add the bacon to the pan and cook until golden brown and crispy, 3-4 minutes.
Add the shallots to the pan and cook until tender, 3-4 minutes. Stir the vinegar, beer and Worcestershire into the skillet and reduce by half, about 1 minute. Stir in the mustard and add the spinach to the pan, tossing to wilt. Season with salt, pepper and nutmeg.
When the spinach is almost completely wilted, dip the sliced beef into the pot of warm stock to heat it through, 3-4 minutes.
To serve, arranged the wilted spinach on a plate and top with some sliced steak, croutons, and crispy bacon.