What you have described is, by default, how Flask works. My assumption is that you are running in debug mode, and therefore exceptions are being shown to you in the debug screen. Make sure debug mode is off, then try again. Here is a comment directly from the code itself:
Default exception handling that kicks in when an exception occurs that
is not caught. In debug mode the exception will be re-raised
immediately, otherwise it is logged and the handler for a 500 internal
server error is used. If no such handler exists, a default 500
internal server error message is displayed.