Step 1

In a 10-inch cast iron skillet, heat oil over medium heat until just starting to shimmer. Add sliced garlic and cook, stirring frequently, until garlic is golden brown all over, about 7 minutes, taking care not to let any garlic pieces burn. Remove garlic and reserve.

Step 2

Add spinach to skillet, season with salt, and cook, tossing frequently, until wilted and mostly dry, about 5 minutes. Turn off heat, add remaining 1 clove minced garlic, and stir until minced garlic becomes fragrant, about 30 seconds. Add sesame oil and vinegar and toss to combine. Transfer spinach to plate and wipe out the skillet with clean kitchen towel (no need to wash).

Step 3

If Using Chicken Breasts: Return skillet to medium-high heat and heat until just starting to smoke. Meanwhile, smear chicken skin with thin layer of mayonnaise, if using (if not, proceed with recipe). Season breasts with salt, then add to skillet, skin side down; for optimal browning, place a cooking weight on top of each breast (optional). Cook until skin is well-browned and crisp, about 5 minutes. Flip breasts, lower heat to medium-low and continue to cook until thermometer inserted into thickest part of the breast registers 150°F (65°C), about 6 minutes. Transfer breasts to plate to rest.

Step 4

If Using Chicken Thighs and Drumsticks: Return skillet to medium-high heat and heat until just starting to smoke. Meanwhile, smear chicken skin with thin layer of mayonnaise, if using (if not, proceed with recipe). Season chicken with salt, then add to skillet, skin-side down; for optimal browning, place a cooking weight on top of each piece of chicken (optional). Cook until skin is well-browned and crisp, about 6 minutes. Flip chicken and continue to cook until thermometer inserted into thickest part of thighs and drumsticks registers 160°F (71°C), about 1 minute longer for the drumsticks and 3 minutes longer for the thighs. As each piece of chicken reaches its doneness, transfer to a plate to rest.

Step 5

Meanwhile, add sake to skillet and cook, scraping up any brown bits on the bottom of the skillet, until sake no longer smells of alcohol, about 1 minute. Add dashi, soy sauce, mirin, and reserved sliced garlic. Bring liquid to boil, then reduce heat to medium-low and let simmer until slightly reduced and garlic cloves are fully cooked, about 4 minutes. Add cornstarch slurry in small increments to the skillet, pausing between each addition to let the mixture thicken a bit. When sauce has thickened slightly (you may not need all the slurry), turn off heat and add butter to pan, swirling and stirring until it is fully melted and incorporated into the sauce.

Step 6

To Assemble the Bowl: Place a shy 1 1/2 cups of rice into each serving bowl. Top with kizami nori (if using). Slice chicken into 1/4-inch-wide slabs (if using breasts) or 1/4-inch-wide deboned strips (if using thighs and drumsticks) and distribute evenly in each bowl. Spoon sauce over rice and chicken. Distribute cooked spinach and garlic cloves evenly in each bowl. Top each bowl with raw egg yolk, if using, and garnish with sliced scallions and pickled ginger (if using). Serve immediately, with any excess sauce passed alongside.