Preheat the oven to 350°.
Place the spinach in a clean kitchen towel (not terrycloth), gather the edges together and twist to wring dry. Use your fingertips to loosen and fluff up the spinach.
In a medium skillet, heat the oil, two turns of the pan, over medium to medium-high. Add the butter; let it melt. Add the shallots and garlic and cook, stirring often, until softened, about 3 minutes. Sprinkle in the flour and cook, stirring constantly, until blended, about a minute more. Add the milk; bring to a bubble. Season with salt, pepper and the nutmeg. Stir in the spinach and cook, stirring often, until heated through, about 3 minutes. Stir in the cheese and reduce the 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 to 5 minutes. Cut the rolls in half horizontally, but not all the way through, leaving a hinge.
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.