If you're using Safari browser on a Mac, you'll find that Safari has a default setting that automatically unpacks zip files.

When you download EasyRecipe, your browser will unpack it and that's not what you want. WordPress requires a zip file to be able to use the standard WordPress plugin installer.

Not to worry, there's a cure for it!

You can turn off the default setting from Preferences > General in Safari and unchecking “Open ‘safe’ files after downloading

Once you’ve changed that setting, you can download the EasyRecipe Plus zip file and then install it by uploading it in the WordPress plugin installer.