Season meat on all sides with salt, pepper, and your favorite beef or steak seasoning.
Heat oil in a large skillet over high heat until shimmering. Place meat in the pan to sear for 2 minutes on each side, turning carefully with tongs. Transfer the seared roast to the slow cooker.
Add onion, garlic, and beef broth to the slow cooker, then cover with lid and cook on LOW for 8 hours until meat is tender.
Meanwhile, make noodles by whisking the eggs, milk, oil, and salt together in a medium bowl. Add 1 cup of flour, stirring it into the liquids with a fork. Continue to add remaining flour ¼ cup at a time until the dough comes together in a slightly sticky ball. It might not take all of the flour.
Turn the noodle dough onto a lightly floured surface and knead by hand for 3-4 minutes until no longer sticky. Let rest for 10 minutes, then roll out very thin using a rolling pin. Cut into thin strips. The noodles can be made in advance and refrigerated for up to 4 days or placed in a ziploc bag and frozen for up to 3 months.
Once the beef is tender, remove it from the slow cooker and shred the meat using two forks, discarding any large pieces of fat. Return the meat to the slow cooker, then add the noodles a handful at a time, stirring gently so the noodles don't stick together.
Increase the heat to HIGH, then cover and cook another 30-45 minutes until the noodles are cooked through. Serve hot either by itself in a bowl or poured over mashed potatoes. Garnish with chopped fresh parsley, if desired.