Pat the chicken dry and season generously with salt and pepper.
Sear chicken until brown on both sides in the dutch oven. This should take about 5 minutes per side.
Take chicken out of the pan and set aside on a plate.
Add the leeks, garlic, a pinch of salt, a pinch of black pepper, and cinnamon. Stir well, making sure to scrape up the brown bits at the bottom of th pan. Cook until leeks are translucent.
Add in the brussels sprouts and stir until combined. dijon mustard and thyme. Stir well.
Pour in the apple cider and mix until everything is well combined. Make sure all of the brown bits from the bottom of the pan have been scraped up. Cover and bring the sauce to a boil. Lower the heat, and add back in the chicken. Cover and let simmer for 15 minutes, or until the chicken is fully cooked through.
Take the chicken, brussels sprouts, and thyme sprigs out of the pan. Set the thyme aside, and place the chicken and brussels sprouts on the desired serving dish.
Add maple syrup to the sauce and bring to a high simmer over medium-high heat. Whisk frequently until the sauce has become thick enough to coat the back of a spoon, this should take around 5-8 minutes. Taste and adjust mustard, sea salt, and black pepper based on desired taste.
Pour the sauce over the chicken. Garnish with bacon and thyme and serve warm!