Coat the diced beef in the flour and set aside. Place the diced potatoes and finely chopped onion into the bottom of the slow cooker.
To make the sauce, whisk together the massaman curry paste, chicken stock, coconut cream, fish sauce, lemon juice and brown sugar until runny and dissolved.
Pour the massaman curry sauce over the potatoes and onions then add in the floured beef. Do not stir.
Put on the lid and cook on low for 8 hours.
Serve on cooked rice, sprinkle with chopped coriander.