Why can't I output the value of my promise in Ember?

I have a property that returns a resolves promise with a string like return Promise.resolve('foo'); Then in handlebars:

<link rel="stylesheet" href=>

Logs:

Promise {__ember_meta__: Meta, [[PromiseStatus]]: "resolved", [[PromiseValue]]: "foo"}

And outputs:

<link rel="stylesheet" href="[object Promise]">

How can I get the value?