Heat 1 tablespoon of oil in a large heavy-based pot over medium-high heat.
Brown the beef cubes in batches until seared on all sides, then remove and set aside.
Add the remaining oil to the same pot and sauté the onions for 8 minutes until golden brown.
Add the vindaloo paste and cook for 2 minutes until fragrant.
Stir in the crushed tomatoes, apple cider vinegar, beef stock, brown sugar, and salt.
Return the beef and any accumulated juices to the pot and bring to a gentle simmer.
Reduce heat to low, cover, and cook for 1 hour and 30 minutes, or until the beef is fork-tender.
Adjust seasoning if necessary and serve hot over basmati rice.