Sprinkle some salt and pepper on the chicken thighs, add the coarsely-ground black pepper, and thoroughly yet gently massage into the meat. Combine the ☆ ingredients.
Add the chicken and the combined ☆ ingredients to a ziploc or plastic bag. Remove the air as much as possible and seal tight. Let marinate for 3 hours, to overnight. Let rest for over an hour at the very least.
Place the chicken on a baking pan with aluminum foil or parchment paper and bake in the oven on the upper rack at 230 ℃ for 20 to 25 minutes. Watch it as it bakes and adjust accordingly.
You can use the leftover marinade. While the chicken is baking bring it to a boil in a small pot. Or microwave until it's simmering.
Once the chicken has been cooked through to the center and is golden brown it's done. It's the most delicious when it's just a tad crispy on the edges.
Transfer to a serving plate and top with the sauce you made in Step 4 (optional). Eating it while it's hot and fresh out of the oven is the happiness of homemade cooking.
If you have any sauce left over, marinate a boiled quail egg together with the green onion, ginger, and you'll get a flavored boiled egg. It's good for lunch boxes.
Story Behind this Recipe
I made this for Christmas this year. I was looking through the ingredients in store-bought sauce and realized that mentsuyu could be used to season roasted chicken.
If you have the time, marinate for as long as possible, overnight is the best. Let the flavors settle in at least for an hour. However, if you top with the sauce you can get it to work out. Adjust the baking time and brown color accordingly, so it cooks through to the center.