Pat the chicken thighs dry and place in a bowl. Combine beer, chopped rosemary, minced garlic, crushed red pepper, salt and black pepper. Pour marinade over chicken, toss to coat, cover and refrigerate for 30–60 minutes (can be up to 2 hours). Reserve the marinade liquid.

Braising & Sauce

Sear

Heat olive oil in a large wide skillet or Dutch oven over medium-high heat until shimmering. Remove chicken from marinade (reserve liquid) and sear pieces 2–3 minutes per side until golden-brown but not fully cooked. Work in batches if needed. Transfer seared chicken to a plate.

Build the sauce

Reduce heat to medium. Add the sliced onion to the same pan and cook, stirring occasionally, until softened and beginning to brown, about 6–8 minutes. Stir in tomato paste and cook 1 minute. Pour in reserved marinade (including beer) and the chicken stock, scraping any browned bits from the pan. Add vinegar, brown sugar and bay leaf. Bring to a gentle simmer.

Braise

Return the seared chicken to the pan, nestling into the sauce. Partially cover and simmer gently for 20–25 minutes until chicken is cooked through and very tender (internal temperature 165°F / 74°C). If liquid reduces too quickly, add up to 1/4 cup extra stock or water.

Shred

Remove chicken pieces to a cutting board, discard the bay leaf. Using two forks or tongs, shred the chicken into bite-sized pieces. Return shredded chicken to the pan and toss with the sauce. Taste and adjust seasoning with salt, pepper or another pinch of crushed red pepper if desired. Simmer together 3–5 minutes so flavors meld and sauce thickens slightly.

Finishing & Coating

Toast breadcrumbs

While the chicken finishes, melt the butter in a small skillet over medium heat. Add breadcrumbs and toast, stirring, until golden and crisp, about 3–4 minutes. Stir in chopped parsley and lemon zest, then remove from heat.

Serve

Spoon the shredded drunken chicken into a serving bowl. Sprinkle the toasted breadcrumbs evenly over the top and finish with a light dusting of red pepper flakes if desired. Serve hot with crusty bread, rice, polenta or over pasta to soak up the spicy beer sauce.