Michele's stuffed Mushrooms with cheese and prosciutto

1 LB mushrooms, cleaned and caps removed
1/2 LB prosciutto diced
8 oz cream cheese
4 oz cheddar cheese grated
1 stick of butter

add all the ingredients into a 3 qt stock pot, except for the mushrooms.  Melt over medium heat, stirring constantly.  Spoon melted mixture into each mushroom cap place on cooking sheet with a lip to collect juice, bake 350 degrees for 8 to 10 minutes until done.  These mushrooms can also be baked on a grill covered with foil.  Serve with toothpicks.