Cut the beef into 1-2 inch cubes and add to the slow cooker.
Blend together the sauce ingredients and pour into the slow cooker. Cook on high for 4 hours or low for 6-8 hours.
Once the cook cycle has ended, add the last teaspoon of garam masala and the heavy cream. Stir well to combine. Turn the cooker on to high heat for 15-30 minutes (or transfer it all to a pot and heat it to a simmer over medium-low heat). Once heated through, top with cilantro if desired and serve with rice or naan and samosas.