Heat a large saute pan over medium high heat. Sprinkle salt and pepper over the beef cubes and place them in the hot pan. (Do this in batches if necessary so the cubes are not crowded.) Sear the beef cubes on all sides, 1-2 minutes per side. Remove the meat from the pan and place it in a large, 3-4 quart slow cooker.
Melt ½ tsp of butter in the, now empty, pan. Add onions and garlic. Sauté over medium heat until golden, 7-10 minutes. Transfer the onion mixture to the slow cooker.
Melt the remaining ½ tsp butter in the pan. Add the carrots, bell peppers, and potato. Sauté over medium heat, 7-10 min. Add the Hungarian paprika and caraway seeds. Mix well. Transfer the mixture to the slow cooker.
Put 1 c of water into the hot pan to deglaze the pan. Scrape up any stuck bits and seasonings from the pan, and then pour the liquid into the slow cooker.
Add the bay leaf to the slow cooker along with enough water to just barely cover the meat. Cover and cook on low for 6-8 hours (or high for 4 hours).
About 30 minutes before serving the soup, add the diced tomatoes. Mix the soup well. Taste it and add salt as desired, to taste. If the soup is too brothy for your liking, continue cooking with the lid off until the desired thickness is reached.
Serve the soup with crusty, whole grain bread.