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Slow Cooker British Chicken and Leek Casserole (Creamy, Comforting & Effortlessly Good)

A rich and deeply comforting Slow Cooker British Chicken and Leek Casserole made with tender boneless chicken thighs, sweet silky leeks, carrots, celery, and a creamy sauce finished with crème fraîche and wholegrain mustard. A classic British family dinner that is completely hands-off and ready with barely any effort — perfect for busy weeknights and outstanding for batch cooking.

  • Total Time: 7 hours 15 minutes
  • Yield: 4–6 servings 1x

Ingredients

Scale
  • 800g boneless, skinless chicken thighs
  • 3 medium leeks, washed and sliced into 1.5cm rounds
  • 2 medium carrots, peeled and sliced
  • 2 celery stalks, sliced
  • 1 medium onion, finely diced
  • 3 cloves garlic, minced
  • 200g chestnut mushrooms, sliced (optional)
  • 400ml good quality chicken stock
  • 2 tbsp wholegrain mustard
  • 1 tsp dried thyme
  • 1 tsp dried tarragon
  • Salt and black pepper
  • 2 tbsp cornflour mixed with 3 tbsp cold water (to thicken)
  • 150ml full-fat crème fraîche
  • Small handful of fresh parsley, roughly chopped

Instructions

  1. Wash and slice the leeks, carrots, celery, and onion. Place all the vegetables into the slow cooker pot and spread into an even layer.
  2. Season the chicken thighs generously on both sides with salt and black pepper and place on top of the vegetables.
  3. In a jug, whisk together the chicken stock, wholegrain mustard, dried thyme, dried tarragon, garlic, salt, and pepper. Pour evenly over the chicken and vegetables.
  4. Place the lid on the slow cooker and cook on LOW for 6–7 hours or HIGH for 3–4 hours until the chicken is completely tender and cooked through.
  5. Using two forks, shred the chicken gently into chunky pieces directly in the pot. Mix the cornflour with cold water to form a smooth slurry and stir into the slow cooker. Cook on HIGH for a further 15–20 minutes until the sauce has thickened.
  6. Turn off the slow cooker. Stir in the crème fraîche and fresh parsley until the sauce is creamy and smooth. Taste and adjust seasoning generously.
  7. Serve ladle over creamy mashed potatoes with warm crusty bread on the side.

Notes

  • Always wash sliced leeks thoroughly to remove any grit trapped between the layers.
  • Do not lift the lid during cooking — each lift adds 20–30 minutes to the cook time.
  • Add crème fraîche only after turning off the slow cooker to prevent it splitting.
  • Add 150g smoked bacon lardons (fried until crispy) for an exceptional smoky variation.
  • Leftovers make a spectacular chicken and leek pie the following day — top with puff pastry and bake at 200°C for 25–30 minutes.
  • Store in the fridge for up to 4 days or freeze for up to 3 months.
  • Reheat gently in a saucepan with a splash of stock if the sauce has thickened too much.
  • Author: Sarah Thompson
  • Prep Time: 15 minutes
  • Cook Time: 7 hours
  • Category: Main Course
  • Method: Slow Cooker
  • Cuisine: British

Nutrition

  • Serving Size: 1 serving (without mashed potatoes)
  • Calories: 385
  • Sugar: 5 g
  • Sodium: 510 mg
  • Fat: 20 g
  • Saturated Fat: 8 g
  • Unsaturated Fat: 10 g
  • Trans Fat: 0 g
  • Carbohydrates: 12 g
  • Fiber: 3 g
  • Protein: 38 g
  • Cholesterol: 135 mg

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