Marinade your chicken pieces by combining: 1/4 cup plain yogurt, 2 teaspoons lemon juice, 1 teaspoon of each of these -crushed ginger, crushed garlic, garam masala, ground coriander. Cover and leave to marinade for at least 10 minutes.
Heat up a skillet on the stove, add a little ghee or coconut oil. Cook your chicken pieces in 2 - 3 batches for a couple minutes to sear / brown the edges. Don't worry if the chicken isn't cooked through. It will finish cooking in the slow cooker.
Pop the chicken in the slow cooker and add your sliced onions, a little ghee or coconut oil to your hot pan. Fry for a couple minutes until soft. Add the remaining garlic, ginger and spices to the pan and fry for 1 - 2 minutes, stirring to stop any sticking to the bottom of the pan. (See Note 1). You will start to smell the flavors developing.
Add the onion and spice mix to your chicken in the slow cooker.
Stir in the tomato puree and coconut milk.
Cover the Slow Cooker and cook for 2 - 3 hours on high.
Serve with cooked brown rice. (See Note 2) and top with a dollop of plain yogurt (optional) and fresh coriander.
Notes
For a hotter curry, add 1/4 to 1 teaspoon of freshly sliced Chili or Cayenne Pepper at this stage. Start with less, taste before adding more.
I like to make a quick salad with sliced red onions, baby tomatoes, cucumbers and coriander to serve on top of my curry. If you want a little more heat, you can include some chopped fresh chilies too.
Olive oil has a lower smoke point than ghee or coconut oil, so I don't use it for high temperature cooking.