Clean any large bits of fat or tendon from the 550 grams boneless skinless chicken thighs and cut into large chunks. Sprinkle with 1 teaspoon salt and ¼ teaspoon ground black pepper and mix to distribute evenly.
550 grams boneless skinless chicken thighs, 1 teaspoon salt, ¼ teaspoon ground black pepper
Heat the 1 tablespoon vegetable oil in a heavy bottomed pot over medium-high heat until hot and shimmering and then add the chicken in a single layer. Let the chicken brown undisturbed (about 5 minutes). Flip the chicken and let it brown on the other side.
1 tablespoon vegetable oil
Turn down the heat to medium-low and transfer the chicken to a bowl using tongs, making sure to leave as much oil in the pan as possible.
Add the grated 14 grams garlic and 14 grams fresh ginger and fry in the oil until it's not sizzling as much and it reaches a rich caramel brown color.
14 grams garlic, 14 grams fresh ginger
Add the 500 grams onion and stir to coat with oil. Cover with a lid and let the onions steam until translucent and limp (about 10-15 minutes).
500 grams onion
Remove the lid, turn up the heat to medium and continue frying the onion, stirring constantly until it's reduced to about ⅛ of its original volume and it forms a shiny caramel brown paste (about 20-30 minutes). If the onion starts to stick to the pan before it's fully caramelized, try scrubbing off the stuck bits with a spatula. If that doesn't work you can add just a bit of water to the areas where things are sticking and then use the spatula to scrape.
When the onions are fully caramelized, add the 3 tablespoons Japanese curry powder and sauté briefly until very fragrant.
3 tablespoons Japanese curry powder
Return the chicken to the pot and then add the 3 cups low-sodium chicken stock, 300 grams carrots, grated ½ medium apple, 2 tablespoons chunou sauce, 1 tablespoon tomato paste, 1 teaspoon unsweetened cocoa powder, 1 teaspoon salt and 1 bay leaf. Bring to a boil over high heat and then reduce the heat. Cover and simmer for 15 minutes.
3 cups low-sodium chicken stock, 300 grams carrots, ½ medium apple, 2 tablespoons chunou sauce, 1 tablespoon tomato paste, 1 teaspoon unsweetened cocoa powder, 1 teaspoon salt, 1 bay leaf
Add the 350 grams potatoes, cover and simmer until the carrots and potatoes are very tender (another 15-20 minutes).
350 grams potatoes
In the meantime, make the roux by adding the 1 tablespoon cultured unsalted butter and 1 tablespoon all-purpose flour to a small saucepan over medium heat. Use a spatula to stir constantly until the bubbling subsides and the roux is a light brown color.
1 tablespoon cultured unsalted butter, 1 tablespoon all-purpose flour
When the potatoes are tender, taste and adjust salt to taste. If you like your curry sweeter, you can add some honey.
Finish the curry by stirring in the roux and ½ cup frozen green peas and bringing to a boil to thicken the sauce.
½ cup frozen green peas
Serve with hot rice, or on top of a bowl of udon.