Cooking cream is available in cold or shelf packs in supermarkets. It resists splitting when heated. If you must use regular cream in this recipe then add a tsp of corn flour to it first before you add it to help lesson the risk of that splitting.More info on that HERE
At the end of cooking you may find some excess butter risen to top of dish - this can be removed prior to serving. Or, remove potatoes to serving plate, whisk back into sauce and pour over. I found this recipe happily sat on ‘keep warm’ setting for 2hrs after cooking and this settled any butter to the bottom of the cooker that was then easily left behind when plating potatoes :)