In a mixing bowl, add tomato sauce, fresh ginger, minced garlic, molasses, brown sugar, and all the spices. Whisk together well.
Dice onion and place in the crockpot.
Place chicken breasts on the onions.
Pour tomato sauce mixture into the crockpot, over the chicken.
Cover the crockpot with a lid, and cook on low for 6-8 hours.
Several hours before the curry is finished cooking, remove mangoes from the freezer and let them thaw at room temperature.
When mangoes have thawed, blend them to a smooth puree. An immersion blender also works well for this.
30 minutes before the curry is done cooking, remove chicken from crockpot, shred it with forks, then put it back in the crockpot.
Add coconut cream, heavy cream, remaining brown sugar, remaining molasses, and mango puree, giving it all a good stir, then replace the lid and cook remaining 30 minutes.
Enjoy over rice, with naan bread.