In a medium pot of boiling water, blanch green beans for 2 minutes. Remove from heat, drain, and run under cold water to stop the cooking.
In a large skillet cook the bacon until crispy, remove to a bowl lined with paper towel. Let sit to drain grease.
While pan is still hot, add chopped onions and cook 2-3 minutes until onions are translucent. Add in fresh thyme leaves and stir until fragrant, about 1 minute. Add brown sugar and apple cider vinegar, and stir in cooked bacon pieces. Stir to combine and remove from heat.
Place green beans in a 11X7 casserole dish, pour chicken stock into the bottom. Spoon caramelized bacon and onion mixture over top.
Cover with foil and set aside. Reheat beans at 350 degrees for 20 minutes, remove foil for the last 5 minutes to crisp up bacon. Toss and serve hot.