4.2 Without cocoon, simple form or formtastic? Nested Recipe attributes

I struggle with nested forms. There're three classes Recipe, Quantity and Ingredient:

class Recipe < ActiveRecord::Base
  belongs_to :user
  has_many :quantities
  has_many :ingredients, through: :quantities
  accepts_nested_attributes_for :quantities

class Quantity < ActiveRecord::Base
  belongs_to :recipe
  belongs_to :ingredient
  accepts_nested_attributes_for :ingredient, :reject_if => :all_blank

class Ingredient < ActiveRecord::Base
  has_many :quantities
  has_many :recipes, :through => :quantities

Recipe Controller

def new
  @recipe = current_user.recipes.build
  @quantity = @recipe.quantities.build
end
def create
    @recipe = current_user.recipes.build(recipe_params)
    if @recipe.save
      redirect_to @recipe
    else
      render 'new'
    end
end
  private
    def recipe_params
      params.require(:recipe).permit(
        :name, 
        quantities_attributes: [:id, :amount, :ingredient_id],
      )
end

View for recipe#new

<%= form_for @recipe, html: {class: "form-horizontal"} do |f| %>
  <li class="control-group">
   <%= f.label :name, "Recipe Name", class: "control-label" %>
   <div class="controls"><%= f.text_field :name %></div>
  </li>
  <%= f.fields_for :quantities do |quantity| %>
    <%= render 'quantity_fields', f: quantity %>
  <% end %>
  <%= f.submit %>
<% end %>

_quantity_fields

<%= f.label :amount, "Amount:" %>
<%= f.text_field :amount %>

Here should follow a Select input with content from Ingredient and the POST request should insert the ingredient_id in the column of Quantity.

<%= f.fields_for :ingredient do |quantity_ingredient| %>
  <%= quantity_ingredient.text_field :name %>
<% end %>

Any ideas? Thanks!