Prepare the onions: bring a large oven safe pan to low/medium heat. Add the butter and 1 tablespoon of olive oil. Once the butter has melted add your onions. Stirring every few minutes, cook the onions on low heat (about 20 minutes) until they're golden, soft, and jammy. If they start to stick to the pan you can add a splash of water or broth. Once the onions are nearly done, preheat your oven to 425 °F.
Prepare the chicken: while the onions are cooking, prepare the chicken. To a large bowl add the chicken thighs, 2 tablespoon olive oil (save 1 tablespoon to fry the chicken), balsamic vinegar, garlic, dried thyme, salt and pepper. Mix until well combined and set aside until ready to use.
Finish the onions: once golden in colour, add your balsamic vinegar, dried thyme, salt and pepper. Cook for an additional minute. Remove onions from the pan, and set aside.
Fry the chicken: to the same pan set to medium/high heat, add 1 tablespoon of olive oil. Fry the chicken thighs on each side for 1-2 minutes or until golden brown. Don't worry about cooking the chicken all the way through as it will finish cooking in the oven. Remove the chicken from the pan and set aside.
Prepare the orzo: to the same pan, add the uncooked orzo and lightly toast for 1-2 minutes on low/medium heat. Add the caramelized onions, chicken stock and heavy cream. Bring to a light simmer, stirring often, then turn off the heat. Next, nestle in the chicken thighs and cover with aluminum foil.
Bake: for 20-30 minutes, or until orzo and chicken are fully cooked.
Garnish: with fresh parsley or green onions if desired.