Preheat oven to 350°F.
In a medium skillet, heat the oil, two turns of the pan, over medium-high. Add the butter; let it melt, then add the shallots and garlic, and cook, stirring until softened, about 3 minutes. Sprinkle in the flour and cook, stirring constantly, until blended, about a minute more. Add the milk and bring to a bubble; season with salt, pepper and nutmeg. Stir in the spinach and cook, stirring often until heated through, about 3 minutes. Stir in the cheese and reduce heat to low.
In a large shallow skillet, bring the consommé to a simmer over medium-high, just a minute or two.
Place the bread on a rimmed baking sheet and heat in the oven just until warm and lightly crispy, 2-5 minutes. Cut the rolls in half horizontally, but not all the way through, leaving a hinge at one edge.
Dip each roll in the consommé, turning to coat. Using tongs, dip the roast beef, a few slices at a time, into the consommé and fill the rolls. Top with the spinach mixture.
Serve extra consommé alongside for dipping.
MORE:
Tournedos with Creamed Spinach Creamed Spinach Fork-and-Knife Burgers Stay Home for a Steakhouse Supper: Roasted Garlic Creamed Spinach