Quails are accommodating little birds. The flesh is moist and tender, and they have a mild flavour that goes well with many types of seasoning.
I used hatcho miso for this dish because I like its strong, rich flavour. If you prefer another type of miso, you can use that, instead.
Use poultry shears to snip off the wingtips from each quail. Cut along one side of the backbone from the tail end to the neck, then turn the quail around and cut along the other side of the backbone to detach it completely. Turn the bird over so the skin side is down. From the cavity, pull out the wishbones, shoulder bones and ribs – on quail, these bones are thin and detach easily. By the time you finish, each quail will have only the bones in the leg (thigh and drumstick), the breast, and those in the middle and drumette portion of the wings. Dry the fleshy parts of the quails with paper towels. Very lightly sprinkle salt over the birds. (The bones can be used to make poultry stock.)
Roughly chop the nashi pear, ginger and garlic. Put the hatcho miso, nashi pear, sake, ginger and garlic in a blender or food processor (or use an immersion blender) and purée to a thick, rough paste. Cut the butter into small chunks, add it to the ingredients and purée again. Mix in the yuzu zest. Smear the paste over the entire surface of the quails then put them in bowl, cover with clingfilm and refrigerate for several hours.
Heat the oven grill (broiler) to high. Lay the quails skin-side down on a lightly oiled grill rack. Slide the rack into the oven so the quails are about 2.5cm (1in) away from the heat element. Cook the quails for five minutes, then flip them over and cook another five minutes, or until done – the flesh will still be slightly pink at the centre, and the skin will be charred in spots. If the skin and meat get too dark before the birds are done, put them a little further away from the heat. Cut the quails into halves or quarters and serve hot or warm.