Preheat the oven to 350 degrees F. Grease 6 ramekin dishes.
Cook the rice according to package directions. Drain and put the pot over low heat for a few minutes to steam the rice dry.
Melt the butter in a large skillet over medium heat and add the mushrooms and onions. Saute them for a few minutes, then push them to 1 side of the pan and add the flour. Stir until the mushrooms and onions are coated with the butter. Add the cream, stirring constantly. Add the sherry and salt and pepper, to taste; stir until smooth. Fold in the cooked rice and pour into the ramekins. Top with bread crumbs and bake until the top is brown, about 15 minutes.