Brown the Beef: Heat 1 tablespoon of oil in a large casserole pot over medium-high heat. Season the diced braising steak with salt and pepper, then add to the pot. Sear the beef for 5-8 minutes, turning occasionally, until all sides are evenly browned. Transfer the browned beef to a plate and set aside.

Prepare the Base: In the same pot, add the remaining oil and butter, allowing the butter to melt. Add the chopped onion and cook for approximately 15 minutes, stirring frequently, until the onions are softened and golden brown.

Add Aromatics and Spices: Stir in the crushed garlic, grated ginger, chili powder, turmeric, ground coriander, and crushed cardamom pods. Cook the mixture for 2 minutes, stirring constantly, to release the aromas of the spices.

Incorporate Tomatoes and Stock: Add the canned chopped tomatoes, beef stock, and sugar. Stir to combine and bring the mixture to a gentle simmer.

Simmer with the Beef: Return the browned beef to the pot, ensuring it is submerged in the sauce. Cover the pot with a lid and cook over low heat for 1½ to 2 hours, or until the beef is tender and the flavors are well-developed. For a thicker consistency, remove the lid during the final 20 minutes of cooking.

Finish with Garam Masala and Cream: Stir in the garam masala and, if desired, add the double cream for a richer finish. Adjust seasoning with salt and pepper as needed.

Garnish and Serve: Sprinkle fresh coriander over the curry before serving. Serve hot with naan bread or steamed basmati rice.