The day before you plan to serve, in a large bowl, combine the miso and 1/3 cup cold water and whisk until thoroughly combined, smooth and thick.
2
Using a small, sharp knife, peel the ginger. Grate the ginger on the large holes of a box grater. Wrap the grated ginger in a paper towel and squeeze the ginger juice, about 2 tablespoons, through the paper towel into the bowl with the miso. Stir to incorporate.
3
Cut the chicken breasts in half across the width of each breast. Add the chicken to the miso-ginger mixture and turn the pieces to coat thoroughly. Sprinkle the chicken liberally with salt. For a more gingery flavor, you can finely chop the remaining ginger pulp, add it to the chicken, and mix again. Cover and refrigerate for 18 to 24 hours.
4
Preheat oven to 500 degrees.
5
Remove chicken from the bowl, making sure some marinade remains on the chicken, and transfer to a rimmed baking sheet, skin side up. Bake for 10 minutes, then put under the broiler, about 6 inches from the heat, for 1 to 2 minutes, or until the skin is dark golden brown and the chicken is just firm to the touch. (Be careful not to overcook.) Remove the skin (if desired) and serve immediately.
