Persian chicken with caramelized onions and spinach rice

This one-pot "Spinach Tah-chin" recipe is inspired by Yotam Ottolenghi's Chicken with caramelized onion and cardamom rice recipe. To prepare the dish, chicken thighs are first browned and then braised while layered inside a mixture of aromatic rice, spinach, and kefir. For the keen reader, Another Spinach Tah-chin recipe may be found here. 

Ingredients:

2.2 Pounds (~ 1 kg or 4 medium) chicken thighs
1 medium yellow onion, finely chopped
2 cinnamon sticks
1/4 TSP cardamon powder
1/2 TSP turmeric
Pinch of saffron
1 TBSP brown sugar (or honey)
2 cups Jasmine 
3 cups water
1 cup Kefir (or buttermilk or diluted yogurt)
200 gr (7 Oz) fresh spinach leaves

Brown the thighs in a smoking hot non-stick pot. When thighs are golden brown, add the onion and lightly caramelize (dark caramelization would affect the desired yellow color of the final dish and hence should be avoided). To the chicken pot, add the spices, rice, Kefir, and water and then the spinach, reserving a handful of the spinach for a later application.  

Cover the pan and reduce the heat to low. Cook until the surface liquid is evaporated. Uncover the pot and stir. Lay the reserved spinach on top, cover the pot and cook for forty minutes. Do not open the pot as the generated steam is crucial for the proper cooking of the rice.