I use small green French (Puy) lentils in this recipe. Use small, whole lentils rather than the large brown lentils or hulled red lentils. Small whole red lentils or black beluga lentils would also be suitable.
Soak the lentils overnight in a large bowl of water if you remember. This is not a necessary step, but will help the lentils cook faster.
I usually divide this mixture into two 2L dishes, then cook one for dinner and freeze the other pie. A 2L container is slightly larger than you will need, but it stops the pie filling overflowing onto my oven floor.
* The pie can be cooked from frozen, however I prefer to defrost it first. If cooking from frozen, I would add at least an extra 20 minutes to the cooking time.
^ The pie will be gluten free if you use a gluten free plain flour.