Season beef generously with smoked paprika, garlic powder, salt, and pepper. Let stand at room temperature for 15 minutes.
Heat olive oil in a Dutch oven over medium-high heat until shimmering. Working in batches, sear the beef until deeply browned on all sides, about 3-4 minutes per batch. Transfer to a plate.
Reduce heat to medium. Add onions to the pot, scraping up the flavorful brown bits from the bottom. Cook until onions are translucent and golden, about 5 minutes.
Add carrots and celery, cooking until vegetables begin to soften, about 4 minutes. Add garlic and cook until fragrant, about 1 minute.
Return beef to the pot along with any accumulated juices. Pour in broth and tomatoes. Add rosemary sprigs and Parmesan rind if using.
Bring to a gentle boil, then reduce heat to maintain a steady simmer. Cover and cook for 45 minutes or until beef is tender.
Stir in pastina and cook uncovered for 6-8 minutes until pasta is al dente.
Remove rosemary sprigs and Parmesan rind. Season to taste with salt and pepper.