Laravel - class FORM not found,...

Para que el {{ Form::open}} no de el error de "not fouind", debes hacer lo siguiente:

Add the following lines laravelcollective/html": "5.3.* in the require section of your composer.json file and run composer update.

"require": {
. . . .
"laravelcollective/html": "5.3.*"
. . . .
}

than RUN "compser update" on your terminal.

composer update

Next, we need to Register the service provider by default stored on config/app.php by adding the following value into the providers array:

'providers' => [
// ...
Collective\Html\HtmlServiceProvider::class,
// ...
],

Register facades by adding these two lines in the aliases array on config/app.php :

'aliases' => [
// ...
'Form' => Collective\Html\FormFacade::class,
'Html' => Collective\Html\HtmlFacade::class,
// ...
],


Ahora tu puedes usar la clase FORM a tu proyecto.
(Extractado desde: http://www.hc-kr.com/2016/09/laravel-5-tutorial-forms-html-class.html)