Season the beef cubes with salt and pepper. Brown them in a skillet over medium heat for several minutes until the edges turn dark.
Transfer the beef to a slow cooker. Add the carrots, potatoes, onion, and celery.
Stir in the beef broth, tomato paste, and thyme. Cover and cook on low for 7 hours until the beef is tender.
In a mixing bowl, combine the flour, baking powder, and 1/2 teaspoon salt. Stir in the milk, melted butter, parsley, and rosemary until a soft dough forms.
Drop spoonfuls of the dough onto the surface of the stew. Cover and cook on high for 1 more hour until the dumplings are firm and cooked through.