Heat vegetable oil in a large pot over medium heat. Add the diced onions and sauté until translucent, about 5 minutes.
Stir in the diced carrots and minced garlic, cooking for an additional 3-4 minutes until softened.
Add the maral meat cubes to the pot, cooking until browned on all sides, about 8-10 minutes.
Pour in the beef broth, then add the black pepper, salt, thyme, and bay leaf. Bring the mixture to a boil.
Reduce the heat to low, cover, and simmer for about 1 hour, allowing the flavors to meld and the meat to become tender.
After 1 hour, add the chopped ferns to the pot. Continue to simmer for an additional 30 minutes until the ferns are tender.
Taste and adjust seasoning if needed. Remove the bay leaf before serving.
Ladle the stew into bowls and garnish with fresh dill if desired.