Melt two tablespoons of the butter in a large nonstick skillet on medium heat. Add onion and cook until softened.
Add beef and lemon juice. Brown the beef.
Stir in the paprika, minced garlic, garam masala, and cumin; cook and stir for 1 minute.
Mix the cream, tomato paste, and remaining butter in. Add salt and red pepper to taste, if desired. Bring to a simmer.
Reduce heat to low; stirring frequently, simmer 5 minutes or until slightly thickened. Turn to low and simmer until ready to serve.
Optional: Add beef broth to thin the sauce.
Notes
Beef Cubes - You want to use a cut of beef that is already tender. Stew meat or chuck steak will not work because it needs a long time to cook. Beef tenderloin or most other cuts of steak would be fine.