Slow-cooker chicken casserole - Master recipes

Ingredients

• knob of butter -
• ½ tbsp rapeseed or olive oil -
• 1 large onion, finely chopped -
• 1 ½ tbsp flour -
• 650g boneless, skinless chicken thigh fillets -
• 3 garlic cloves, crushed -
• 400g baby new potatoes, halved -
• 2 sticks celery, diced -
• 2 carrots, diced -
• 250g mushrooms, quartered -
• 15g dried porcini mushroom, soaked in 50ml boiling water -
• 500ml stock made with 2 very low salt chicken stock cubes -
• 2 tsp Dijon mustard, plus extra to serve -
• 2 bay leaves -