How to link to controller actions in a Craft 3 plugin?
Apparently I figured it out. Would still like a better way of doing this, but here's the solution I found to be working:

In your Plugin class, you have to add a public $controllerMap array. For my example plugin above, here's what I would have to add to that $controllerMap array:

use Very\Waffle\Controllers\SyrupController;

class Plugin extends \craft\base\Plugin
{

    /** @var array */
    public $controllerMap = [
        'syrup' =&gt; SyrupController::class,
    ];

    // other code here, obviously
}