How do I include and iframe in a Custom Block?

Given the html block tag I can include and iframe from Google My Maps in my post.

I need to create a block where the client can paste the URL from the embed code and the block render the iframe.

note: embed code does not mean using the embed tag, but that is what the iframe code is called to embed the map on a web page.

I have attempted with Genesis Custom Blocks but it will not render the iframe.