The tender steak and soft shallots are ideal partners in this sandwich. They're also great over mashed potatoes with a simple arugula salad on the side.
Pat steaks dry with paper towels and season with salt and pepper.
In a large skillet, heat oil over high. Cook steaks until medium-rare, about 4 minutes per side. Transfer to a cutting board and tent loosely with foil.
Reduce heat to medium, add shallots, and cook until softened, 8 minutes.
Add cream and 2 tablespoons water and cook, stirring, until slightly thickened, 1 minute. Stir in mustard and season with salt and pepper. Thinly slice steak against the grain. Make sandwiches with rolls, shallots, steak, and arugula.
Feel free to try this recipe with chicken cutlets; turkey cutlets, halved horizontally; or pork tenderloin, cut into 1-inch slices and pounded 1/4 inch thick.