When roasting, make sure you are not overcrowding your pan. Make sure there is enough space so your potatoes do not overlap on top of each other, which would encourage steaming instead of roasting. After your potatoes have roasted, they will soften a little when stored. Make sure that your potatoes have cooled completely before placing in an airtight container in the fridge. If you’d like to bring back their crispiness, place in a toaster oven or air fryer for a few minutes to warm them through and help crisp up their edges again.