For the chicken paprikash: Preheat the oven to 400 degrees F.
Season the chicken with one-third of the paprika (1 tablespoon plus 1 teaspoon), 1 tablespoon salt and some pepper.
Heat the oil and chicken fat or butter in a large ovenproof pan over medium heat. When hot, add the chicken and brown for 2 minutes per side; remove to a plate. Add the onions, cabbage and remaining paprika (2 tablespoons plus 2 teaspoons) and cook, stirring occasionally, until starting to soften, 3 to 4 minutes. Add the flour and cook the roux, stirring, for 2 minutes. Stir in the stock, making sure there are no lumps.
Return the chicken to the pan skin-side up. Bake until the chicken is cooked through and measures 160 degrees F, 20 to 35 minutes.
For the spaetzle: While the chicken is cooking, bring a saucepan of water to a boil.
Sift the flour and 1 teaspoon salt into a bowl. Make a well and mix in the eggs and milk.
Dampen a plastic cutting board and place the dough mixture on it. Cut off strips of dough into the water and cook for 3 minutes. Drain the spaetzle and rinse under cold water. Set aside until the chicken is done.
Add the spaetzle to the chicken pan, stir in the sour cream and parsley if using and serve.
For more ingredient substitution ideas, see the article below.