Season the beef chuck cubes with salt and freshly cracked black pepper.

Heat 3 tablespoons of neutral oil in a large pot or Dutch oven over medium-high heat.

Brown the beef cubes in small batches until they are evenly seared on all sides. Once browned, take the beef out of the pot and set it aside.

In the same pot, reduce the heat to medium and add the chopped onion.

Sauté until softened, about 4-5 minutes.

Stir in the minced garlic and sauté for an additional 1 to 2 minutes until it becomes aromatic.

Stir in the garam masala, cumin, paprika, turmeric, ground mustard, cayenne pepper (if using), ground ginger, and cinnamon.

Toast the spices in the onion mixture for 1-2 minutes, stirring constantly, until the spices are fragrant.

Stir in the tomato paste and cook for another 1 minute to caramelize it slightly.

Pour in the apple cider vinegar and cook for 2-3 minutes, stirring to deglaze the pot and scrape up any browned bits from the bottom.

Add 1 cup of low-sodium beef stock, ensuring the beef is mostly covered in liquid.

Bring the mixture to a simmer, cover, and reduce the heat to low.

Cook for 1.5 to 2 hours, or until the beef is tender, stirring occasionally and adding more beef stock if needed to keep the beef submerged.

Taste the sauce and adjust the seasoning if needed (add salt, pepper, or a splash more vinegar for tang).

If you prefer a thicker sauce, remove the lid during the last 20 minutes of cooking to allow the sauce to reduce.

Serve the beef vindaloo hot with cooked basmati rice and warmed naan.

Optionally, offer a dollop of plain Greek yogurt on the side to help balance the spiciness.