When baked correctly, the edges should appear golden while the centre remains lightly golden, producing the classic chewy edge and tender middle. Store in an airtight container for up to five days, layering pieces with parchment to prevent sticking. To freeze, layer with parchment in an airtight container or freezer bag and thaw at room temperature or in the refrigerator. Use only porridge oats or rolled (old-fashioned) oats; avoid steel-cut or instant varieties, which alter texture and structure unfavourably.