In a suitable saucepan over medium heat, melt the butter Once hot, add the onions and sauté until tender but not browned, about 2 minutes Stir in the peppers and mushrooms and sprinkle with salt and pepper Cook another 3 to 4 minutes, until tender.
Add the roast beef and toss to mix well Stir in the broth and bring to a simmer Cook 10 minutes.
Place the cream cheese in a blender and add about ¼ of the hot broth from the pan Blend until smooth and the cream cheese is melted Pour the mixture back into the pan and stir in the shredded cheese until melted.
Preheat the broiler Ladle the soup into oven safe bowls or ramekins and top with a piece of provolone Set on a baking sheet and place under the broiler until the cheese is melted and bubbly, 2 to 4 minutes.
Serve immediately.