Start by preparing the chicken and cutting it into bit size pieces.
Next, add the salt, pepper, chili powder, coriander, turmeric, kasoori methi, garlic, ginger, yogurt, and lemon to a large bowl along with the prepared chicken and mix thoroughly. Cover the bowl with plastic and keep it in the refrigerator to marinate for 1 hour.
While the chicken is marinating, start on the sauce.
Add 2 tablespoons of unsalted butter to a large rondeau pot over low to medium heat and caramelize the red onions until they are well browned, which takes about 30 minutes. Stir every 5 to 6 minutes.
Next, mix in the ginger and garlic, and cook until the garlic is fragrant, which takes about 30 to 45 seconds.
Add in the garam masala, chili powder, ½ teaspoon of kasoori methi, dried chiles, and jalapaño, and mix for 1 to 2 minutes. You may need to add some water to scrape up some of the fond. See chef notes.
Place in the tomatoes and cashews, stir and cover with a lid, and cook for 20 minutes on low to medium heat. Come back every 5 to 7 minutes to give it a quick stir.
Next, transfer the mixture to a blender and blend on high speed until smooth.
Strain the mixture back into the pot and keep warm on low heat. See chef notes on thinning out.
Whisk in 1 stick of cold butter until mixed in and then add in the whipped cream and stir to combine.
Adjust the seasonings of the sauce with salt. Keep warm.
In a separate large rondeau or frying pan with ghee or oil over medium-high heat, add the marinated chicken once the butter or oil begins to smoke lightly.
Spread the chicken out across the pan and cook the chicken for 3 to 4 minutes, and then stir-fry for 1 to 2 minutes or until cooked throughout. See chef notes on searing.
Transfer the cooked chicken to the pot with sauce and finish by mixing in fresh chopped cilantro, remaining ½ teaspoons of kasoori methi, and 2 tablespoons of butter and serve.
Notes
Make-Ahead: This is meant to be eaten immediately; However, you can keep warm in the sauce on low heat for up to 30 minutes before serving.How to Store: Cover and keep the butter chicken in the refrigerator for up to 5 days. This will freeze well covered for up to 3 months. Thaw it in the refrigerator for 1 day before reheating.How to Reheat: Add the desired amount of butter chicken to a small saucepot and heat over low heat until hot.You can marinate the chicken overnight. However, I do not think it needs to go that long as the marinade is jam-packed with flavor and can infuse into the chicken in a short amount of time.After the 5th procedure, it’s good to deglaze with 3 to 4 tablespoons of cold water to release the fond. Fond is the browned bits of food remaining on the bottom of a pan after it has been sauteed or roasted.When blending anything hot, be sure to remove the centerpiece to the lid of the blender to release the heat, or else it will explode. I usually place a towel over the top while blending.To thin out the sauce after blending, add about a cup of cold water to the blender and swish it before straining. The sauce will remain thick and have a good consistency.If you want to get a good sear on the chicken, you’ll need to do it in batches to spread it out and ensure the pieces aren’t touching each other.