Heat butter in a large cast iron-skillet and sauté onions until tender and transluscent. About 5 minutes.
Add heavy cream and bring to a boil; reduce heat and stir in the cheese. Continue to whisk until the cheese has melted, add parsley, and fold in cooked spaetzle. Season to taste with salt and pepper.
OPTIONAL - For a crispy curst, place the cast iron skillet for 2-3 minutes under the broiler.
Notes
If you live near Aldi's, you might be able to find pre-cooked spaetzle.
CAST IRON SKILLET
If you don't plan on putting the cheese spaetzle under the broiler, you don't need to use a cast iron skillet.