How to connect window from outside window to inside wall.

[AlexDiversified]

So I have a concrete outside wall. I made it a pony wall to be able to edit the siding on the outside. In reality its a full concrete wall. I have to frame a wall inside the concrete wall for framing the house. So i have a window in the wall which goes through the concrete and the inside wall. As you can see in the picture theres a gap between the inside wall window cut out and the window outside. How do i remove this gap so it looks like a regular window with a deep window sill???

[MarkMc]

Make the interior wall furred.