Make the sauce: In a small pan cook the onion in the butter with the paprika over moderately low heat, stirring, until it is softened. Stir in the flour and cook the roux, stirring, 2-3 minutes. Add the broth and vinegar and simmer the sauce, stirring, for 2 minutes. Cover and keep warm.
In a bowl whisk together the egg, milk, 1 tbls water, salt and pepper. Add the flours and beat the mixture with a wooden spoon until it is just smooth.
"Grate" the dough into boiling salted water. Cook until spaetzle floats.
Add spaetzle to the sauce and cook over moderate heat, stirring, until it its heated through, and stir in the parsley.
This will make two healthy servings, but, of course, can be doubled or even tripled.
Usually, when I make spaetzle, I make it earlier and hold it in a bowl of cold water. Then I make whatever sauce at the last minute (quite often this is just a sage butter), drain the spaetzle and add it to the sauce, stirring until it's heated through.