Filling around new window

[rshort1987]

Hi
So a while back we had new windows fitted. I have come to decorate one of the rooms and discovered that the internal edge of one window was crumbling. I pulled it all off and have attached pictures of what I am left with. I'm wondering what the best way is to fix/fill this to 'make good'?

Any advice?

Thanks

 

[rshort1987]

I'm mainly thinking about the bigger hole at the top, would expanding foam work in there? and then use a filler all the way down?

 

[foxhole]

Foam could be used , or bonding plaster for the deeper areas toppe off with filler to sand back .