Step 1
Place lamb shanks in a large resealable plastic bag. Whisk together cider vinegar oil salt tamarind concentrate and garam masala in a bowl and pour into the bag. Squeeze out excess air and seal the bag. Marinate in the refrigerator for 8 hours or overnight.
Step 2
Preheat an oven to 450 degrees F (230 degrees C). Grease a foil-lined baking sheet.
Step 3
Remove marinated lamb shanks and place on the prepared baking sheet. Season all sides with salt. Roast in the preheated oven until well-browned 15 to 20 minutes. Reserve marinade in the bag.
Step 4
Combine 1 onion garlic ginger cherry tomatoes and water in a blender and pulse on and off until smooth. Set aside.
Step 5
Combine cayenne pepper paprika cinnamon cumin dried mustard and black pepper in a small bowl.
Step 6
Melt clarified butter in a large stockpot over medium-high heat. Cook and stir 1 onion until softened and well-browned about 30 minutes. Reduce heat to medium and pour in cayenne pepper mixture. Cook and stir until spices are aromatic about 2 minutes.
Step 7
Pour marinade from the bag into the stockpot and stir in tomato-onion mixture and brown sugar. Bring mixture to a simmer. Place lamb shanks in the pan and reduce heat to low. Cover and cook turning occasionally until meat is tender and easily pierced with a fork 3 to 4 hours.
Step 8
Remove lamb from the pot and cover with foil. Increase heat and simmer the sauce for a few minutes skimming the fat from the top. Taste and add salt if needed. Serve lamb shanks with sauce spooned over the top. Garnish with cilantro.