Grease a 1-1/2 qt. casserole.
Melt butter in top of a double boiler; remove from heat.
Add flour and blend well, then add milk.
Place over boiling water, stirring until smooth.
Cook, stirring, until thickened.
Add cheese and stir until melted.
Beat eggs separately, whites first.
Add beaten yolks to cheese mixture gradually, stirring constantly.
Add salt, paprika, and onion.
Fold in stiff egg whites and turn into prepared casserole.
Set oven temperature to 375 degrees F. and preheat for 10 minutes.
Place pan of water in oven 5 minutes before setting soufflé in the warm water. The soufflé will come up fast, but bake it for the full 40 to 50 minutes.