Meanwhile, in 3-quart saucepan or Dutch oven, melt butter over low heat. Cook mushrooms and garlic in butter, stirring occasionally, until mushrooms are tender. Stir in flour, salt and pepper. Cook over medium heat, stirring constantly, until mixture is smooth and bubbly. Gradually stir in milk, sherry and broth until smooth. Heat to boiling, stirring constantly. Stir in Fontina cheese until melted; remove from heat.