Make your tentsuyu. You can use my recipe, or there are a number of recipes on the app, but it's usually something like 3-4 parts dashi with 1 part each soy and mirin.
Peel about a 1 inch knob of ginger. A great way to peel ginger is with s teaspoon. Helps you quickly get into all of the little crevices.
Then, grate your ginger. They make tools for this exact purpose, usually a sort of flat surface with little bumps on it. That's the ideal tool, but I used a microplane.
Combine ginger, chicken, and tentsuyu. Mix it up and seal it tight. Put it in the fridge and let it marinate for a few hours.
Cook these guys however you like. Chicken thighs are quite forgiving, so don't worry too much if you've never worked with them before. Toss them on a hot grill or a bake on a foil-lined sheet tray at 450f or so. When you can slice into the widest part of a big thigh and it's not pink, then you're ready to serve. You could also slice em up and throw them in a stir-fry.
