Grind black pepper, mustard seed and allspice. Mix all the ingredients together until the chicken thigh is uniformly covered with the spices and herbs mixture. Using two same sized baking trays turned on top of each other or a big enough dish with a lid then shake until everything is covered, can be a quite effective method. Once the chicken thighs are covered evenly, it's ready to be put in the oven but for better results, let them marinade do its thing. 1 - 24 hours in the fridge can do wonders, the more the better.
If it is not done earlier, turn the chicken thighs upside down. Place them on the middle rack of a 390°F / 200°C preheated oven until the internal temperature of the chicken reaches 175°F – 180°F / 79°C – 82°C which should happen in 30 - 45 minutes. We can, of course, keep them in longer if we are after a less chewy, juicy but softer texture.
Take the tray out and flip the chicken thighs over then put them back to one of the upper shelf of the oven.
Set the temperature to maximum, using only the top heat source of the oven, many ovens are equipped with a broiler so use that. Roast the chicken thighs to crispy perfection. Keep a close eye on them as this can happen in 1 - 15 minutes, depending on the closeness of the thighs to the heat source and the exact temperature. If some protruding parts seem to catch way more heat than its good for them, just lower the heat or the tray so the skin roasts evenly.