Hibachi Chicken with Yum Yum Sauce

Steps

1. Start with the yum yum sauce, since it improves as it sits. Melt 15 g of the butter in the microwave for 20 seconds. Whisk the mayonnaise with the ketchup, the warm melted butter, the rice vinegar, 1 teaspoon of the sugar, the paprika, and the garlic powder until the sugar no longer feels gritty. Cover and refrigerate for at least 30 minutes: the spices hydrate and the sauce turns its signature salmon orange.
2. Rinse the rice in cold water, rubbing it between your fingers, 4 or 5 times, until the water runs almost clear. Drain for 10 minutes, then put it in a heavy-bottomed saucepan with the 360 ml of water. Bring to a boil, cover, turn the heat to the lowest setting, and cook for 12 minutes. Turn off the heat and let it steam for 10 minutes without lifting the lid.
3. Meanwhile, cut the chicken into 1 inch (2.5 cm) cubes, trimming off any large pieces of fat. Pat them thoroughly dry with paper towels, then season with salt and pepper. Cut the zucchini into 1/2 inch (1 cm) half-moons, the onion into 3/4 inch (2 cm) squares, and the mushrooms into quarters. Finely mince the garlic and slice the green onion on the bias. In a bowl, mix 3 tablespoons of the soy sauce with the mirin and the rest of the sugar.
4. Toast the sesame seeds in a dry large cast iron skillet or wok over medium heat for 2 minutes, until they turn golden and start to pop. Tip them into a small dish.
5. Turn the heat to high. When a drop of water flicked into the pan beads up and evaporates within a second, add 1 tablespoon of the oil, the onion, and the mushrooms. Let them sear for 3 minutes without stirring so they brown, then add the zucchini and stir-fry for 4 minutes: it should be golden in spots and still firm in the center. Add 15 g of the butter and the last tablespoon of soy sauce, toss for 30 seconds, and keep warm in a dish in a 175°F (80°C) oven.
6. Wipe out the pan with a paper towel and put it back over high heat for 2 minutes, until it smokes lightly. Add 1/2 tablespoon of oil and lay half the chicken in a single layer, with no pieces touching. Leave it alone for 2 minutes: the underside should be golden and release on its own. Flip and sear for 2 more minutes, then transfer to a plate. Repeat with the remaining oil and chicken.
7. Return all the chicken to the pan and lower the heat to medium-high. Add the remaining 30 g of butter and the minced garlic and stir for 30 seconds: the butter foams and the garlic smells fragrant without browning. Pour in the soy-mirin mixture, which bubbles right away, and toss for 1 to 2 minutes until it reduces to a glossy glaze that coats every cube. The largest piece should read at least 165°F (74°C) inside; thigh meat stays tender up to 185°F (85°C).
8. Off the heat, drizzle with the lemon juice and toss one last time, scraping up the browned bits from the bottom of the pan.
9. Fill the bowls with rice, spoon the chicken and its juices on top, and scatter with the toasted sesame seeds and green onion. Serve the yum yum sauce in small dishes and the griddled vegetables alongside on a separate plate, the way they do at the teppanyaki counter.