Roll each slice of bread flat. Brush one side of each slice with melted butter, and press each into an 8-ounce custard cup. Mold bread to side of cup. Bake at 350° for 15 minutes or until lightly browned. Transfer toast cups to a serving platter; set aside.
Melt 1/4 cup butter in a heavy saucepan over low heat; add flour, and stir until smooth. Cook 1 minute, stirring constantly. Gradually add milk and whipping cream; cook over medium heat, stirring constantly, until thickened and bubbly. Stir in salt and egg.
Spoon 1/3 cup mixture into each toast cup. Serve immediately.