For the lamb:
1 T garam masala
1 1/2 t salt
1 t cumin (toast)
1 t coriander (toast)
1/2 t pepper
3/4 lb lamb leg sirloin, in 1 inch cubes
2 c plain whole milk Greek yogurt
3 T oil
4 medium garlic cloves, minced or pressed
2 T grated fresh ginger
Combine garam masala, salt, cumin, coriander, and pepper. Toss with lamb cubes, press gently to adhere. In a bowl, combine yogurt, oil, garlic and ginger. Toss lamb cubes in this, and refrigerate 30-60 minutes. Proceed with the masala sauce.
For the masala:
1/2 c ghee (or oil)
2 T garam masala
2 t salt
2 - 2 1/2 c onion, diced fine
6 cloves garlic, minced or pressed
1 1/2 T grated fresh ginger
2 medium serrano chiles, seeded, ribbed, and minced
2 T tomato paste
1 28 oz and 1 14 oz can diced tomatoes, drained of fluid, fluid saved
1 c coconut milk
2 c cream (or next time I want to do plain Greek yogurt)
If using cream, not yogurt: juice of 1 small lemon or 1 t tamarind paste
Chopped cilantro, to serve
Heat fat in a big pan over medium/medium-high heat until it shimmers. Add onion and salt. Cook to wilt onion, 11-12 minutes, stirring occasionally. Reduce heat to medium low. Add garlic, ginger, chile, and tomato paste. Cook, stirring constantly, until onions have browned completely, approximately 7 minutes. Sprinkle with garam masala and stir to coat. Add tomatoes and, if you like, a little bit of their fluid. I added maybe 3/4 c. Cook, stirring occasionally, until they have reduced slightly and deepened in color, 15-20 minutes. After this, you can hold it on low for a while if you need to.
While sauce simmers, adjust rack to upper middle (6 inches from top) and heat broiler. Arrange the lamb cubes on a wire rack set in a foil lined, rimmed baking sheet. Broil until the exterior is lightly charred and the lamb is yummy. Flip halfway through if you're up to it.
Right before adding lamb, add cream or yogurt and coconut milk. Use an immersion blender to make it as smooth as you can. Adjust the seasoning: salt as needed, and I added more cumin. It is also at this point that I added more cream; my base recipe just had the 1 c. Sour with lemon juice or tamarind if needed. Make it yummy. You could also add pepper, more garam masala, or individual components if you think they are needed: cardamom, coriander, mustard, cloves, chile, cinnamon, nutmeg, etc.
Add the lamb, heat through, and serve over basmati rice and garnished with chopped cilantro.