Heat a knob of butter and ½ tbsp rapeseed or olive oil in a large frying pan,
cook 1 finely chopped large onion for 8-10 mins until softened and starting to caramelise.
Meanwhile, put 1 ½ tbsp flour and a little salt and pepper in a bowl and toss 650g boneless, skinless chicken thigh fillets in it.
Add 3 crushed garlic cloves and the chicken to the pan and cook for 4-5 mins more until the chicken is starting to brown.
Transfer to your slow cooker, along with 400g halved baby new potatoes,
2 diced celery sticks, 2 diced carrots, 250g quartered mushrooms,
15g dried and soaked porcini mushrooms with the 50ml soaking liquid,
500ml chicken stock, 2 tsp Dijon mustard and 2 bay leaves.
Give it a good stir. Cook on Low for 7 hours or High for 4 hours.
Remove the bay leaves and serve with a little Dijon mustard on the side.