Here is a pro tip that changes everything: freeze the filling and the mash separately. I know, it sounds like heresy. But hear me out. When you freeze an assembled pie, the moisture from the mince seeps into the potato. When you reheat it, you get a hybrid layer of brown-grey sludge that offends both the eye and the palate.
Instead, cook your mince, cool it, and pour it into a dish. Then, make your mash—but add an extra yolk and a knob of butter to stabilize it for freezing. Let the mash cool, then pipe or spoon it over the frozen mince. This is the professional move.
Classic cottage pie (meal or freezer prep) - Luvele UK
Alternatively, freeze the mash in a bag and the mince in a block. Assemble on the day of cooking. It is two extra minutes for a vastly superior result.
