In a fry pan, quickly brown the onions and hamburger together. Add the seasonings and continue to sauté for 2 minutes.
Transfer beef mixture to the slow cooker. Add the mushroom pieces and sliced mushrooms. Give it a quick stir and then add the beef broth and the can of soup. Mix well.
Cook on high for 2.5 hours or low for 4 – 5 hours. Stir once throughout the process.
Shortly before serving, boil the pasta to an al dente stage in salted water.
Add the drained pasta and the sour cream and let it cook the remaining 30 minutes.