Heat a large, heavy-based frying pan such as a cast-iron skillet over medium heat. Add the thighs skin side down and cook until the skin is browned – around 6-8 minutes depending on size. Set aside, leaving the fat in the pan.
Slice the onions, smash the garlic, tear the bread into chunks.
Add the onions, garlic and sourdough and season lightly. Place the chicken thighs on top, skin side up and season again. Put in the oven and cook for 30 minutes, or until cooked through.
While the chicken is cooking, make the salsa verde: finely chop the herbs, capers, cornichons, garlic cloves, anchovies & mix together. Add the mustard, vinegar, oil and a little salt if you think it needs it.
Serve the chicken thighs with some of the sourdough, garlic and onions and the salsa verde.