Preheat the oven to 350 degrees F. Butter a 2 quart soufflé dish.

In a heavy saucepan placed over low heat, melt the butter. Whisk in the flour, salt, paprika, and a dash of cayenne.

Pour ½ cup of the hot milk into the flour mixture and whisk in. Add the remaining milk and whisk in well. Add the grated cheese, whisking until the cheese melts. Remove from the stove.

Whisk in the egg yolks.

Finely slice the mushrooms. Fold into the flour mixture.

Sprinkle the egg whites with the cream of tartar and beat with an electric mixer until firm. Fold a few spoons of the mushroom sauce into the egg whites. Continue adding the sauce a few spoonfuls at a time. Always fold in an overhand (hand moving away from you) motion.

Gently pour the mixture into the prepared soufflé dish. Bake for 45 minutes.