Pat the chicken thighs dry with paper towels and season them with 0.5 tsp of the sea salt and 0.25 tsp of the black pepper.
Heat the olive oil in a large heavy-bottomed pot or Dutch oven over medium-high heat.
Sear the chicken thighs in the pot until golden brown on both sides, working in batches if necessary, then remove the chicken and set it aside on a plate.
Add the diced yellow onion, chopped carrots, and chopped celery to the pot and sauté for 5 to 7 minutes until the vegetables are softened.
Stir in the minced garlic and dried thyme, cooking for about 1 minute until the aromatics are fragrant.
Add the cubed sweet potato and pour in the chicken bone broth, using a wooden spoon to scrape the bottom of the pot to release any flavorful browned bits.
Return the chicken thighs and any accumulated juices to the pot, bring the liquid to a boil, then immediately reduce the heat to low and cover with a lid.
Simmer the soup for 20 to 25 minutes or until the chicken is cooked through and the sweet potatoes are fork-tender.
Remove the chicken thighs from the pot, shred the meat into bite-sized pieces using two forks, and return the shredded chicken to the soup.
Stir in the chopped kale and the remaining sea salt and black pepper, simmering for 3 to 5 minutes until the kale is wilted and tender before serving.