Preheat the oven to 400F.

Slice the bread in half lengthwise using a serrated knife. Carefully pull out the insides of the bread, making sure not to go all of the way through. (This will make a sort of "boat" to hold the filling.)

Place the bread, cut side up, on a baking sheet. Toast in the oven for about 5 minutes. Meanwhile, cut each mushroom in half and then thinly slice.

Place a large skillet over medium heat. Remove the sausage from the casings and add to the skillet. Cook until no longer pink, breaking the sausage up as it cooks, about 5 minutes. Sprinkle the flour over the sausage and cook, stirring, for another minute. Add the broth and the mushrooms. Cook, stirring frequently, until the mushrooms have softened, another 5-10 minutes. Remove the pan from the heat and stir in the Parmesan cheese.

Divide the mixture evenly between the two bread halves and spread from end to end. Top each piece with 4 slices of cheese. Place back in the oven until the cheese is melted, about 5 minutes.

Remove from the oven and cut into slices to serve.