Combine sauce ingredients: Use a wide, thick-bottomed pot or Dutch oven that will hold all the chicken pieces in one single layer. Place the water, soy sauce, rice vinegar, Gochujang paste, honey, chili flakes, and pepper into the pot. Whisk well.
Cook chicken: Skin the chicken pieces and arrange them in the pot in a single layer. Bring to a boil, reduce heat to medium, and simmer, covered, for about 15 minutes.
Prepare vegetables: In the meantime, peel and chop the potatoes into large chunks. Cut the carrots and the onion into chunks as well. Peel the garlic cloves and chop them finely. Peel and grate the ginger.
Cook vegetables: Add the prepared vegetable to the pot and stir to make sure that they are all mixed in the sauce. Cover again and cook for further 15 minutes or until the potatoes are tender.
Remove the lid from the pot and continue cooking for about 10 minutes until the chicken is cooked through and the sauce is slightly thickened.
Thicken sauce: If you like your sauce to be thicker, you can thicken it with a small amount of cornstarch slurry. Mix 1 tablespoons corn starch with 1-2 tablespoons cold water to form a thick yet still runny paste. Whisk this slurry into the boiling sauce, let bubble shortly, and remove the pot from the heat.
Adjust taste: Stir in the sesame oil, check the seasoning, and sprinkle the chicken stew with chopped scallions and toasted sesame seeds just before serving.