Boil the chicken breast until cooked through, about 20-30 minutes. Use a hand mixer to finely shred the chicken. Season with salt and pepper, to taste and set aside.
In a soup pot over medium high heat, add two tablespoons of butter. Saute the onions and carrots until tender, about 5-10 minutes. Add in the minced garlic.
Sprinkle the flour over the contents of the pot and add the remaining butter to form a simple roux. Stir constantly until the flour and butter is coating the onions and carrots.
When the roux is golden, season with paprika, cayenne pepper (optional), sugar and white pepper. Deglaze the bottom of the pot with the sherry, scraping up any browned bits on the bottom.
Pour in the chicken broth and bring to a rolling bubble. Simmer for 30 minutes.
Reduce the heat to medium and add the spaetzle and shredded chicken. Simmer for 10 minutes to cook the spaetzle and heat the chicken through.
Stir in the Greek yogurt and remove from heat. Serve garnished with a dollop of yogurt and parsley for a pop of color. Enjoy!