Pat the beef sirloin tips dry with a paper towel and season them evenly with the sea salt and black pepper.
Heat the ghee in a heavy-bottomed pot over medium-high heat and sear the beef until a golden-brown crust forms on all sides.
Remove the beef from the pot and set aside, then add the diced carrots, celery, and onion to the remaining fat.
Sauté the vegetables for 5-7 minutes until softened, then stir in the minced garlic, dried thyme, and tomato paste until fragrant.
Pour in the beef bone broth, scraping the bottom of the pot to release any flavorful browned bits.
Return the beef to the pot, bring to a gentle boil, then reduce heat to low and cover with a lid.
Simmer for 25 to 30 minutes until the beef is tender and the liquid has slightly thickened.
Stir in the baby spinach just before serving until it is wilted and bright green.