in one fell swoop

in one fell swoop
at one fell swoop

If you do something at/in one fell swoop, you do it all at the same time (одним ударом, одним махом, в один момент; разом; за один раз)

Examples: I got all my Christmas shopping done in one fell swoop. (CALD)

More examples:

To turn one complex organism into another complex organism in a single step – as in a fairytale – would indeed be beyond the realms of realistic possibility. And yet complex organisms do exist. So how did they arise? How, in reality, did complicated things like frogs and lions, baboons and banyan trees, princes and pumpkins, you and me come into existence?
The answer is that complex organisms – like humans, crocodiles and Brussels sprouts – did not come about suddenly, in one fell swoop, but gradually, step by tiny step, so that what was there after each step was only a little bit different from what was already there before. Imagine you wanted to create a frog with long legs.
(Richard Dawkins)