Step 1Heat the oven to 400 degrees. Dissolve the dry mustard in one-half teaspoon water and blend into 6 tablespoons of the Dijon mustard. Set aside.
Step 2Working on one hen at a time, cut down either side of the backbone with kitchen shears or a sharp knife and remove the backbone. Lay the hen out, skin side up, on a work surface and press down hard on each side of the breastbone to butterfly the bird. Season on both sides with salt and pepper.
Step 3Heat 2 tablespoons oil in a large skillet over medium heat. Add the hens, skin side down, and cook 4 to 5 minutes on each side, until the birds take on some color (if the pan is too small, cook one at a time). Remove the hens to a platter and keep warm.
Step 4Wipe out the skillet and add the remaining oil. Add the garlic, onion, thyme and potatoes. Season well with salt and pepper. Cook, stirring often, until the vegetables are softened, about 8 minutes. Stir in the parsley.
Step 5Spread the potato mixture in a roasting pan or 9- by 13-inch glass baking dish just large enough to hold both hens in one layer. Arrange the birds on top, skin side up. Brush the skin of each evenly with the mustard mixture. Sprinkle evenly with the panko to coat. Drizzle with the melted butter.
Step 6Roast the hens 25 to 30 minutes, or until the juices run clear when a thigh is pricked.
Step 7As the hens cook, whisk the remaining 1 tablespoon Dijon mustard with the coarse mustard, ketchup, A-1 sauce, Worcestershire sauce and Tabasco to taste.
Step 8When the hens are cooked, run them briefly under the broiler to crisp the coating if necessary. Serve them with the sauce on the side.