In a large bowl, combine the chicken thighs with minced garlic, sliced onions, lemon juice, Dijon mustard, smoked paprika, cayenne pepper, and salt. Ensure the chicken is well-coated in the marinade. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or overnight for deeper flavor.

After marination, remove the chicken from the bowl, scraping off any solids to prevent burning. Pat the chicken dry to ensure it browns nicely. Set aside the marinade and chopped onions for use later.

Heat a large skillet over medium-high heat and add olive oil. Once the oil shimmers, place the chicken thighs in the skillet, cooking for about 4-5 minutes per side until golden brown.

Lower the heat to medium and add the reserved onions and remaining marinade to the skillet. Stir frequently for about 5 minutes until the onions soften and caramelize.

Return the browned chicken thighs to the pan and add chicken broth, ensuring the chicken is partially submerged. Bring to a gentle simmer, cover, and cook for 15-20 minutes.

Remove from heat and allow the Poulet Yassa to sit for a few minutes before serving. The sauce should be thick and rich.