Season and sear the chicken. Mix all spice blend ingredients. Pat the chicken dry and toss with 1 tablespoon olive oil, half the spice blend, 2 minced garlic cloves, and a squeeze of lemon. Let sit 10 minutes. Heat a Dutch oven over medium-high, add olive oil, and sear the chicken 2 to 4 minutes per side until golden. Do not cook through. Remove to a plate.
Build the potato base and par-cook. In the same pan, add more olive oil and butter if using. Add the onion and potatoes in a single layer. Season with remaining spice blend. Cook 5 minutes, stirring to coat. Add remaining garlic and tomato paste, cook 1 minute. Pour in broth, lemon juice, and red wine vinegar. Scrape up the browned bits. Cover and simmer on stovetop 10 to 12 minutes.
Add chicken and bake. Preheat oven to 375 degrees F. Nestle chicken on top of potatoes. Spoon a little sauce over the top. Cover and bake 20 to 25 minutes. Uncover and bake another 10 to 15 minutes until chicken reaches 160 degrees F and the top has color.
Rest and serve. Rest 5 minutes before serving. Finish with fresh parsley.