Melt the butter in a medium saucepan over medium heat. Stir in the minced shallot and cook, stirring frequently, until softened and translucent (this takes about 2 minutes). Stir in the cornstarch and cook for an additional minute.

Add the beef broth, stirring vigorously with whisk until well blended with the cornstarch mixture

Taste the sauce and add salt and pepper as necessary.

Separate the slices of roast beef and add to the sauce. Cook over low heat until the slices are warmed.

Preheat the Panini Press. You should do this for at least 10 minutes before using it.

Divide the cheese and roast beef evenly among the baguettes. Reserve the sauce.

Place the sandwiches on the preheated pan and press down with the panini press. Cook for two minutes on each side.

Serve the Panini with a bowl of the reserved sauce and enjoy!