aliases.erb

<% @aliases.keys.each do |al| -%>
  <%= al %>
  - <%= @aliases[al].join(",")%>
<% end -%>

default.rb

email_alias "thom" do
  address "thom"
  recipients %w{ foo bar baz }
end

email_alias "test" do
  address "test"
  recipients %w{ cat bodge baz }
end

email_alias.rb

resource_name :email_alias

property :address
property :recipients, Array

default_action :create

action :create do
  with_run_context :root do
    edit_resource(:template, "/tmp/aliases") do
      source 'aliases.erb'
      variables[:aliases] ||= {}
      variables[:aliases][address] ||= []
      variables[:aliases][address] << recipients
      action :nothing
    end
  end
  log "force delayed notification" do
    notifies :create, "template[/tmp/aliases]", :delayed
  end
end

gistfile1.txt

     Starting Chef Client, version 12.14.89
       resolving cookbooks for run list: ["test_acc::default"]
       Synchronizing Cookbooks:
         - test_acc (0.1.0)
       Installing Cookbook Gems:
       Compiling Cookbooks...
       Converging 2 resources
       Recipe: test_acc::default
         * email_alias[thom] action create
           * log[force delayed notification] action write


         * template[/tmp/aliases] action nothing (skipped due to action :nothing)
         * email_alias[test] action create
           * log[force delayed notification] action write


         * template[/tmp/aliases] action create
           - create new file /tmp/aliases
           - update content in file /tmp/aliases from none to d822d0
           --- /tmp/aliases	2016-10-10 18:02:35.046372765 +0000
           +++ /tmp/.chef-aliases20161010-6012-ofxf23	2016-10-10 18:02:35.046372765 +0000
           @@ -1 +1,3 @@
           +  thom
           +  - foo,bar,baz,foo,bar,baz

       Running handlers:
       Running handlers complete
       Chef Client finished, 5/6 resources updated in 01 seconds
       Finished converging <default-ubuntu-1604> (0m2.70s).
-----> Kitchen is finished. (0m4.08s)