Season the chicken: Pat chicken thighs dry. Season both sides with salt and black pepper.

Sear the chicken: Heat oil in a large skillet over medium-high heat. Add chicken thighs and sear about 4 minutes per side until golden brown. Transfer chicken to a plate/bowl.

Cook the bacon: Add chopped bacon to the same skillet and cook until browned and crisp. Transfer bacon to a bowl, leaving the bacon fat in the skillet.

Caramelize the onions: Add chopped onions to the skillet and cook 8–10 minutes, stirring occasionally, until softened and golden.

Build the flavor base: Stir in salt, black pepper, thyme, Dijon mustard, whole peppercorns, and garlic. Cook for about 30 seconds, stirring, until fragrant.

Thicken the sauce: Sprinkle flour over the onion mixture and stir well until fully combined.

Add stock + bacon: Slowly pour in hot chicken stock while stirring continuously to prevent lumps, scraping up any browned bits. Return cooked bacon to the skillet and stir.

Simmer: Return chicken thighs and any juices to the skillet. Add bay leaves. Reduce heat to low, cover, and simmer gently for about 40 minutes, until chicken is very tender and the sauce thickens.