When I make a change to the a aspx.cs page in my website and then build I notice that none of the `dll`s in the Bin folder are updated, the only dlls I can see in there are the references the web app uses. I want to bring across this one change rather than redeploy the whole site so where are the changes being saved? 

I've tried various things like build solution, rebuild solution, build website, rebuild web site.

Is it possible my dll is being sent elsewhere? How would I go about finding out where?