Heat a large non-stick skillet over medium-high heat. Add the oil and potatoes along with a few generous pinches of salt; saute for 3 to 5 minutes, until the potatoes begin to brown. Add the onions and saute for another 3 minutes to soften and brown.

Add the garlic, paprika, and cayenne (if using); stir well. Immediately add the broth and wine to prevent the paprika from burning. Stir in the tomatoes and bring the mixture to a boil.

Add the butter. Reduce the heat to medium and simmer uncovered for 15 to 20 minutes, or until the potatoes are very tender. Turn off the heat and stir in the sour cream. Taste and add salt and pepper to your liking.