Preparation

Step1: Marinate the beef

1. In a large bowl, combine the beef chunks with vinegar, ginger-garlic paste, turmeric, chili powder, ground cumin, ground coriander, and salt.
2. Mix well to coat the beef evenly with the marinade. Cover and refrigerate for at least 2 hours, preferably overnight, for the flavors to infuse.

Step2: Prepare the spice mix (if making fresh)

1. Heat a dry skillet over medium heat and toast cumin, coriander, mustard, fenugreek seeds, dried chilies, cloves, cinnamon, and cardamom until aromatic.
2. Grind the toasted spices into a fine powder using a spice grinder or mortar and pestle. Set aside.

Step3: Cook the onions

1. Heat oil in a heavy-bottomed pan or Dutch oven over medium heat.
2. Add the chopped onions and sauté until golden brown. This step is crucial for the depth of flavor in the curry.

Step4: Add the tomatoes and spices

1. Stir in the tomato puree and cook until the oil starts to separate from the mixture, indicating that the rawness of the tomatoes has been cooked out.
2. Add the Vindaloo spice mix, paprika, and slit green chilies. Mix well and cook for another 2-3 minutes.

Step5: Add the marinated beef

1. Add the marinated beef to the pan and stir to coat it with the spice mixture.
2. Cook on medium heat for 5-7 minutes until the beef starts to brown slightly and absorbs the spices.

Step6: Simmer the curry

1. Pour in the beef stock or water and bring the mixture to a gentle boil.
2. Lower the heat, cover, and simmer for 45-60 minutes, or until the beef is tender. Stir occasionally and add water if the curry becomes too thick.

Step7: Adjust seasoning

1. Add vinegar, salt, and additional spices as needed to balance the flavors. Simmer for another 5 minutes.

Step 8: Garnish and serve

1. Garnish with freshly chopped cilantro leaves and serve hot with rice, naan, or bread of your choice.