Set a large soup pot or Dutch oven over medium-high heat and add the olive oil.

Pat the chicken thighs dry with paper towels. Season both sides with the 1 teaspoon salt and 1/2 teaspoon black pepper.

Put the chicken into the hot pot in a single layer. Cook for 3 to 4 minutes on the first side, until browned in spots.

Turn the chicken and cook the second side for 2 to 3 minutes more. Transfer the chicken to a plate; it does not need to be fully cooked yet.

Lower the heat to medium. Add the chopped onion and sliced celery to the same pot.

Cook the onion and celery for 4 to 5 minutes, stirring now and then, until they soften and the onion looks glossy.

Add the garlic and dried thyme to the pot. Stir for 30 seconds, just until the garlic smells fragrant.

Add the potatoes to the pot and stir so they pick up the onion mixture.

Pour the chicken broth into the pot. Use a wooden spoon to scrape up any browned bits stuck to the bottom so they melt into the soup.

Return the chicken and any juices from the plate to the pot.

Raise the heat to high and bring the soup to a boil.

Once the broth boils, lower the heat to maintain a gentle simmer. Partly cover the pot and cook for 15 to 18 minutes, until the potatoes are tender when pierced with a fork and the chicken is cooked through.