They are a poured concrete so the sinks are integrated into the countertop and it is all set as one piece at the time of installation. Let me know if you need a source.

I love the Timberhill Masterbath concrete countertop. How do find a company in my city?

Cavezza do a google search for concrete countertops for your area or try and find a contractor here on houzz in your area just be prepared to pay more than your common granites as concrete countertops here in KC area start at $85/sf and most sinks incorporated into the countertop start at $600 and go up from there.