Preheat oven to 375°F. Butter 6 (6 oz.) ramekins using 1 Tbsp.butter. Set aside.
Melt remaining butter in saucepan and stir in flour. Cook 2 minutes. Whisk in milk until smooth. Remove from heat. Add egg yolks and mix thoroughly. Stir in cheese and prosciutto.
In another bowl, beat egg whites until stiff peaks form. Fold the egg whites gently into the sauce mixture.
Divide mixture among ramekins. Place in oven and bake 20 to 25 minutes. Do not open the oven door during baking time as they will deflate.