Generously salt and pepper the pork. Place a dutch oven or other heavy bottomed pot over medium high heat until hot. Add a tablespoon of oil and when it starts to shimmer, add the pork in a single layer with a little space between each piece. You want to get a nice brown crust on the meat, so if it's too crowded, this won't happen. Let the meat brown on one side until it's not sticking to the pot anymore (about 5-7 minutes). When there's a nice brown crust forming flip the pork over and brown the other side. Repeat if necessary, then set the pork aside in a bowl.
Turn down the heat to medium low, add the onions and garlic, and then cover with a lid. The onions should release moisture which will keep it from burning but check periodically to make sure. Cook with the lid until the onions are translucent and tender (about 20 minutes). Uncover and allow the accumulated moisture to burn off. Continue sautéing until the onions are about 1/4 of their initial volume, and they are a medium brown color all the way through. These browned onions along with the brown crust on the meat is where much of the flavor for this stew comes from, so while it may take a while it's important.
Return the pork to the pot along with the peppers, tomatoes, sauerkraut and paprika. Loosely cover with a lid and braise until the pork is fall-apart tender. Adjust salt and pepper to taste.
In a small bowl, mix the sour cream and flour. Add the hot stock from the pot into the sour cream mixture a spoonful at a time, mixing between each addition. This tempers the sour cream and prevents it from curdling. When the sour cream mixture is steaming hot, pour it back into the pot and stir to combine. When it starts to slightly thicken, it's done.