1. Heat olive oil in a saucepan over medium heat. Add chopped onions and sauté until translucent, about 5 minutes.
2. Add minced garlic and cook for another minute.
3. Stir in the crushed tomatoes, and season with salt and pepper.
4. Simmer for 15-20 minutes, stirring occasionally, until thickened.

Prepare the Chicken

1. Dust the chicken pieces with flour to help create a golden crust when searing.

Sear the Chicken

1. In a large skillet, heat sunflower or grapeseed oil over medium-high heat. Once hot, add the chicken pieces and sear each side for about 3-4 minutes until golden brown. Sear in batches if necessary to avoid overcrowding the pan.

Deglaze the Pan

1. Transfer the seared chicken to a medium-sized pot. Return the skillet to the stove and pour in 1 cup of cider. Scrape the bottom of the pan with a wooden spoon to release any browned bits and let the cider simmer for about 1 minute.

Begin the Braise

1. Pour the deglazed cider over the chicken in the pot. Add the remaining 1 cup of cider, the sliced leek, tomato sauce, and bay leaf. Stir gently to combine.

Simmer the Chicken

1. Cover the pot halfway with a lid and simmer on low heat for 2 hours, stirring occasionally to ensure even cooking and melding of flavors.

Finish the Sauce

1. After 2 hours, stir in the heavy cream. For a thicker sauce, increase the heat slightly and simmer uncovered until it reduces to your desired consistency.

Garnish and Serve

1. Once the chicken is fully cooked and the sauce is to your liking, remove from heat. Garnish with chopped parsley or chives if desired, and serve hot.