Prepare the chicken: Pat the chicken thighs dry and place them in a large bowl.
Make the marinade: Add the sliced onions, minced garlic, lemon juice, Dijon mustard, smoked paprika, cayenne pepper, bouillon powder, and salt. Mix thoroughly so the chicken is coated.
Marinate: Cover and refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to penetrate the chicken.
Separate the chicken: Remove the chicken from the marinade. Scrape off the onions and marinade, keeping them in the bowl because they will be used later.
Brown the chicken: Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the chicken and brown for about 4–5 minutes per side. The chicken does not need to be fully cooked at this stage.
Caramelize the onions: Remove the browned chicken and add the reserved onions and marinade to the pan. Reduce the heat to low or medium-low and cook for about 5 minutes, stirring occasionally, until the onions begin to soften and caramelize.
Combine everything: Return the browned chicken to the pan, nestling the pieces into the caramelized onions.
Cook the chicken: Pour in the chicken broth. Cover and simmer for 15–20 minutes, or until the chicken is fully cooked and the sauce has developed a rich, savory flavor.
Adjust and serve: Taste the sauce and add more salt if needed. Serve the Poulet Yassa Recipe hot with fluffy rice and plenty of the caramelized onion sauce.