On , I learnt ...

How to enable Docker BuildKit in MacOS Docker Desktop

Since Docker 18.09, you can the BuildKit feature to take advantages of improved performance and extra features when building images — see Build images with Buildkit from the Docker docs.

MacOS users using Docker Desktop, can enable this be update the Docker daemon JSON config file to:

{
    "experimental": false,
    "debug": true,
    "features": {
        "buildkit": true
    }
}

This is done via the Preferences > Docker Engine menu option in the GUI.

(This is accurate as of Docker Desktop v3.0.3)