(defun my-buffer-face-mode-pick-font ()
  "Pick a font family using Helm and apply it to the current buffer."
  (interactive)
  (let ((font (helm :sources (helm-build-sync-source "Font Family"
                               :candidates (sort (font-family-list) #'string<)
                               :action (lambda (candidate) candidate))
                    :buffer "*helm-font-picker*")))
    (when font
      (setq buffer-face-mode-face `(:family ,font))
      (buffer-face-mode))))