Cut the beef chuck into approximately 2-inch cubes and place the pieces in a large mixing bowl.
Season the beef with salt and freshly cracked black pepper. Toss gently until the beef is evenly coated.
Heat a large skillet over medium-high heat. Add the neutral oil and swirl to coat the bottom of the skillet.
Once the oil is hot and shimmering, add the seasoned beef. Sear for about 6 minutes, turning as needed, until browned on all sides.
Transfer the browned beef to a plate or bowl and set aside. Keep the skillet and its flavorful browned bits for the sauce.
Reduce the heat to medium. Add the chopped onion and cook for about 15 minutes, stirring frequently, until deeply golden and caramelized. Watch carefully so the onion does not burn.
Add the minced garlic and cook for about 2 minutes, stirring frequently, until softened and fragrant.
Add the garam masala, cumin, paprika, turmeric, ground mustard, cayenne pepper, ground ginger, and cinnamon. Stir constantly for about 1 minute until the spices become fragrant.
Add the tomato paste and stir until it is thoroughly combined with the onion and spices.
Pour in the apple cider vinegar to deglaze the skillet. Cook for 2 to 3 minutes, scraping the browned bits from the bottom as you stir.
Pour in the beef stock and stir gently to combine. Return the browned beef and any accumulated juices to the skillet.
Bring the mixture to a gentle boil, then reduce the heat to medium-low.
Cover the skillet and simmer for about 60 minutes. Stir occasionally and turn the beef pieces as needed for even cooking.
If the sauce becomes too thick while simmering, add 1 to 2 tablespoons of beef stock at a time until it reaches the desired consistency.
Check the beef for tenderness. Once tender and fully cooked, taste the sauce and adjust the salt if needed.
If the vinegar tastes particularly sharp, stir in ½ to 1 teaspoon packed brown sugar and simmer for another 2 to 3 minutes to balance the flavors.
Remove the skillet from the heat. Serve the Beef Vindaloo over cooked basmati rice with warm naan and a spoonful or two of plain Greek yogurt, if desired.