Heat a large pan or wok over medium-high heat. Sear the beef in portions without adding fat, about 3-4 minutes per batch, until well browned on all sides. Set aside.
In the same pan, melt the ghee over medium heat. Add the onion strips and cook for 2-3 minutes, stirring occasionally, until lightly golden. Stir in the curry paste (about 3 tablespoons, or to taste) and mix well for 1 minute. Add the canned tomatoes and stir to combine.
Return the seared beef to the pan. Reduce heat to medium and simmer for about 1 hour, stirring occasionally. Add water if the curry becomes too thick.
Put the cleaned and chopped parsnips in a saucepan. Cover with water and bring to a boil over medium-high heat. Reduce to medium and cook for about 12-15 minutes until very soft. Drain well. Using an immersion blender, puree the parsnips until smooth. Stir the puree into the curry. Stir in most of the chopped coriander, reserving a few fresh leaves for garnish.
Serve with naan or rice, garnished with reserved coriander leaves.