I will have two egress windows cut into my concrete basement walls (9"
thick), will use standard 48" x 48" slider or casement windows.

Two contractors told me they simply frame the freshly cut concrete
with 2 inch "green pressure treated lumber" and then set the window.
(They will do more for a header if needed for space alignment or
structural needs.)

But just a singe 2" board sound too fast and easy.
Is there a "proper" way or am I must use to doing things the hard way?

Thx
Dave-in-Denver