New Twiddle

components.footer-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['footer']
});

components.header-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['header']
});

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

{{#my-component as |comp|}}
  {{#comp.header}}
  	head
  {{/comp.header}}
  {{#comp.footer}}
  	foot
  {{/comp.footer}}
{{/my-component}}
<br>
<br>

templates.components.my-component.hbs

<div class="modal">
  {{yield 
      (hash 
         header=(component "header-component")
         footer=(component "footer-component")
      )
  }}
</div>

twiddle.json

{
  "version": "0.11.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.11.0",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.11.0",
    "ember-testing": "2.11.0"
  },
  "addons": {}
}