First make sure that requests to blot.development go to localhost. You can't just use the hosts file since it doesn't support wildcard entries. I followed this guide so user subdomains work as expected:
It involved installing Dnsmasq using homebrew, then configuring it to resolve all requests to .development to localhost. Then I had to tell OSX's DNS resolver to pass requests to .development to Dnsmasq. Phew!
You need to generate a self-signed certificate and key pair then tell your system to trust it. I then load the key.pem and cert.pem files into the webserver.
Since Chrome 58, you need to declare a Subject Alternative Name. I don't really understand what that is or why it is neccessary but it is.