Prepare and bake the macaroni as above (omitting the breadcrumbs), then remove from the tins and let cool completely. Arrange on a parchment-lined baking sheet and freeze until firm then transfer to a resealable plastic bag or airtight container and freeze for up to 1 month. To reheat, arrange the mac and cheese bites on a parchment-lined baking sheet, sprinkle with breadcrumbs and bake in a 350°F oven until warmed through.