Heat 2 Tbsp. of the ghee in a large saucepan over medium heat. Salt lamb on all over, then sear the lamb on all sides until browned. Remove lamb from pan and set aside.
Fry the cardamom, cinnamon stick, and peppercorns until aromatic, adding an additional 1 Tbsp. of the ghee if pan is dry.
Add onions to pan, reduce heat to medium-low, and fry, stirring as needed to prevent burning.
Add ginger and garlic paste and fry briefly until aromatic.
Return lamb to pan along with any accumulated juices.
Add the chile powder, ground ginger, and ground coriander, stirring to coat the meat.
Add water and yogurt, stirring to incorporate.
Bring to a simmer, cover, and reduce heat to low. Continue cooking until meat is fully cooked.
Heat 2 Tbsp. of ghee in a small pan over medium-low heat. Add the ratan jot, swirling to infuse. Continue heating until ghee is deep red.
Add the ginger and fennel seed to the ghee. Fry briefly until very aromatic.
Strain spices from oil and pour over top the rogan josh. Stir, remove from heat, and let rest 5 minutes.