This is an expression that people sometimes use in spoken English:

You know what makes them even better is to mix a little salt in with the chocolate.

You know what's interesting is that she didn't even start playing until she was in her late teens, which is almost unheard of.

You know what I miss most about living there is how easy it was to walk everywhere.

This form isn't exactly grammatically correct, so in written English you would write something like:

Do you know what makes them even better? Mixing a little salt in with the chocolate.

What I miss most about living there is how easy it was to walk everywhere.