Start by heating a large Dutch oven or heavy bottomed pot over medium heat. While the pot is heating up, season the chicken with salt and pepper.
Once the Dutch oven is hot, add oil and let it heat up some before adding the chicken pieces. Sear the chicken pieces until browned on all sides, about 5 minutes. Remove the chicken from the pot with a slotted spoon and reserve.
Add the potatoes, carrots, kohlrabi, onions, garlic and ginger to the pot. Stir.
Add the sake, raise the heat to high and scrape up any brown bits left in the pan from browning the chicken. Cook for a few minutes until the alcohol in the sake burns off.
Add the chicken stock, gochujang, red pepper flakes, soy sauce and sugar. Give the pot a stir and bring it to a simmer, then reduce the heat to medium.
Add the reserved chicken back into the pot, stir and continue cooking until the chicken is cooked through and the vegetables are tender. This should take about 15 minutes.
We served this dish in bowls because of the lovely, fragrant (spicy) broth the ingredients are cooked in.
Add rice to the bowl, cover with chicken and vegetables and then spoon in some of the broth. Top with the sliced scallions and serve. Or if you can, wait a bit before serving to let all the flavors meld together and then serve.