The Two-layered Sugar Chest is a blocker in Candy Crush Saga, making its official appearance in level 711. However, it is unofficially introduced, both as starting configuration and appearance, in level 501.
Two-layered sugar chests are single-tile stationary blockers that take two matches involving sugar keys to open and therefore destroy. Each matched sugar key results in a degrade. After the first degrade, it becomes a sugar chest with no toppings.
These blockers cannot be destroyed by anything other than matches involving the sugar key.
Here is the difficulty of destroying a two-layered sugar chest: