Slice each chicken breast into 3 or 4 large pieces. Melt 2 tbsp (30 mL) butter in a large wide saucepan over medium-high heat. Add half of chicken to pan. Sprinkle with half of cumin. Turn often until chicken pieces are golden, 5 to 6 minutes. Remove to a bowl. Repeat with remaining butter, chicken and cumin. Remove to same bowl.
While chicken is cooking, finely chop peppers, including seeds. They should measure about 3 tbsp (45 mL). Grate ginger and chop coriander.
When all of cooked chicken is removed to a bowl, pour cream into pan. Scrape up and stir any bits from pan bottom into cream to add flavour. Then stir in tomato sauce, hot peppers, ginger and salt. Return all of chicken and juices to pan. Bring to a boil. Then cover and simmer over medium-low heat, stirring and turning chicken occasionally, until chicken is cooked through, 10 to 15 minutes. Stir in coriander and spinach. Heat just to wilt spinach. Remove from heat. Taste and add more coriander, if needed. Fantastic with basmati rice pilaf.
Make ahead
Prepare chicken and sauce. Don't stir in coriander or spinach. Wrap and refrigerate up to 1 day, or freeze up to 2 months. Reheat thawed chicken in microwave on medium or in a saucepan, stirring often, just until hot. Then stir in sauce, coriander and spinach.
Recipe by Dulcet Devotion at https://dulcetdevotion.com/2011/11/08/finally-some-nice-din-dins-butter-chicken/