Newsflash. I do the same thing as the beautiful Nigella: cook loads of onions in advance and freeze. And for the same reason.
And the one thing I feel utterly beaten by when I'm really tired is the idea of peeling and chopping onions. I don't actually find it difficult, but the thought is a daunting one. So, when I have time to spare (usually when I'm avoiding something I should be doing), I peel, chop, and fry onions slowly and gently to a gorgeous mush that can be frozen in cubes and thawed to form the basis for a stew or sauce as needed.
Let me add that I am even lazier than Nigella: I freeze en masse (rather than in cubes)and break off chunks when needed. Just this morning, I made a soup that began with me breaking off a chunk of onions and blithely tossing it into a pot.
Oh yeah, even lazier part 2: I usually do this in the slow cooker (mush) or oven (roasted).
Oh yeah, and it's frugal too if you buy onions when they are cheap (like last week when they were a dollar for three pounds).
Since at least 75% of all recipes (scientific study conducted by moi) begin: saute a chopped onion, this little tip will save you hours and hours each year.
And, since I'm only me and who cares what I do: I present Nigella as your role model. Do what she does.